Annual report pursuant to Section 13 and 15(d)

Long-Term Debt - Additional Information (Detail)

v3.8.0.1
Long-Term Debt - Additional Information (Detail)
12 Months Ended
Mar. 27, 2017
USD ($)
Mar. 10, 2017
USD ($)
Nov. 30, 2016
USD ($)
May 09, 2013
USD ($)
Jul. 02, 2012
USD ($)
Dec. 31, 2017
USD ($)
Location
$ / shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]                
Loss on repurchase of debt instrument           $ 14,607,000    
Minimum EBTDAR to rent ratio           385.00%    
Incremental interest expense           $ 3,100,000 $ 5,500,000 $ 7,800,000
Net expense expected to be reclassified           100,000    
Derivative Instruments and Hedging Activities [Member] | Interest Rate Swap and Interest Rate Cap [Member]                
Debt Instrument [Line Items]                
Derivative asset, fair value of interest rate swap and cap positions           4,700,000    
Derivative Instruments and Hedging Activities [Member] | Interest Rate Swap [Member]                
Debt Instrument [Line Items]                
Derivative liability, fair value of interest rate swap and cap positions             3,700,000  
Derivative Instruments and Hedging Activities [Member] | Other Current Assets [Member] | Interest Rate Swap and Interest Rate Cap [Member]                
Debt Instrument [Line Items]                
Derivative asset, fair value of interest rate swap and cap positions           900,000    
Derivative Instruments and Hedging Activities [Member] | Other Assets [Member] | Interest Rate Swap and Interest Rate Cap [Member]                
Debt Instrument [Line Items]                
Derivative asset, fair value of interest rate swap and cap positions           5,100,000    
Derivative Instruments and Hedging Activities [Member] | Other Assets [Member] | Interest Rate Swap [Member]                
Debt Instrument [Line Items]                
Derivative asset, fair value of interest rate swap and cap positions             2,800,000  
Derivative Instruments and Hedging Activities [Member] | Other Accrued Liabilities [Member] | Interest Rate Swap and Interest Rate Cap [Member]                
Debt Instrument [Line Items]                
Derivative liability, fair value of interest rate swap and cap positions           1,000,000    
Derivative Instruments and Hedging Activities [Member] | Other Accrued Liabilities [Member] | Interest Rate Swap [Member]                
Debt Instrument [Line Items]                
Derivative liability, fair value of interest rate swap and cap positions             4,100,000  
Derivative Instruments and Hedging Activities [Member] | Other Long-Term Liabilities [Member] | Interest Rate Swap and Interest Rate Cap [Member]                
Debt Instrument [Line Items]                
Derivative liability, fair value of interest rate swap and cap positions           $ 300,000    
Derivative Instruments and Hedging Activities [Member] | Other Long-Term Liabilities [Member] | Interest Rate Swap [Member]                
Debt Instrument [Line Items]                
Derivative liability, fair value of interest rate swap and cap positions             $ 2,400,000  
Mortgage Notes [Member]                
Debt Instrument [Line Items]                
Debt weighted average interest rate on note           4.22%    
Number of operating locations related to mortgage financing | Location           10    
Mortgage financing aggregate           $ 52,500,000    
Percentage of operating locations related to mortgage financing           45.00%    
Outstanding mortgage principal balance           $ 419,700,000    
Notes payable due date           between 2018 and 2033    
Required Ratio [Member]                
Debt Instrument [Line Items]                
Minimum EBTDAR to rent ratio           150.00%    
2016 Credit Facility [Member]                
Debt Instrument [Line Items]                
Maturity date of revolving credit facility and floor plan facility     Nov. 30, 2021          
Minimum EBTDAR to rent ratio           385.00%    
2016 Credit Facility [Member] | Required Ratio [Member]                
Debt Instrument [Line Items]                
Minimum EBTDAR to rent ratio           150.00%    
2016 Credit Facility [Member] | Minimum [Member]                
Debt Instrument [Line Items]                
Net income and retained earnings free of restrictions           $ 148,700,000    
2016 Revolving Credit Facility [Member]                
Debt Instrument [Line Items]                
Increased availability under borrowing facility     $ 25,000,000          
Current borrowing capacity           250,000,000    
Maximum borrowing capacity           300,000,000    
Borrowing base           247,600,000    
Letters of credit outstanding amount           17,300,000    
2016 Revolving Credit Facility           75,000,000    
Borrowing availability amount           155,300,000    
2016 Floor Plan Facilities [Member]                
Debt Instrument [Line Items]                
Increased availability under borrowing facility     $ 215,000,000          
Maximum borrowing capacity           1,015,000,000    
Increase in credit facility borrowing capacity           $ 1,265,000,000    
2016 Used Vehicle Floor Plan Facility [Member]                
Debt Instrument [Line Items]                
Allocation of credit facility increase, percentage           30.00%    
7.0% Senior Subordinated Notes Due 2022 [Member]                
Debt Instrument [Line Items]                
Principal amount         $ 200,000,000      
Stated interest rate on debt agreement         7.00% 7.00% 7.00%  
Notes maturity date         Jul. 15, 2022      
Cash paid to extinguish of debt instrument including early redemption premium and accrued and unpaid interest $ 213,700,000              
Loss on repurchase of debt instrument $ 14,600,000              
7.0% and 6.125% Senior Subordinated Notes [Member]                
Debt Instrument [Line Items]                
Double-carry interest expense           $ 700,000    
6.125% Senior Subordinated Notes due 2027 [Member]                
Debt Instrument [Line Items]                
Principal amount   $ 250,000,000            
Stated interest rate on debt agreement   6.125%       6.125% 6.125%  
Notes maturity date   Mar. 15, 2027            
Notes issued at a price of principal amount   100.00%            
Notes issued yield maturity, percentage   6.125%            
Interest payable description           semi-annually in arrears on March 15 and September 15 of each year.    
Notes redemption price percentage of the principal amount           100.00%    
Redemption Price           106.125%    
Notes redemption price percentage of the par value due to change of control           101.00%    
Debt instrument maximum allowed dividends per share | $ / shares           $ 0.12    
Restrictive covenants under credit facilities and 6.125% notes           Specifically, the indenture governing the 6.125% Notes limits Sonic’s ability to pay quarterly cash dividends on its Class A and Class B common stock in excess of $0.12 per share. Sonic may only pay quarterly cash dividends on its Class A and Class B common stock if Sonic complies with the terms of the indenture governing the 6.125% Notes.    
Outstanding principal amount of the 6.125% notes           25.00%    
6.125% Senior Subordinated Notes due 2027 [Member] | Maximum [Member]                
Debt Instrument [Line Items]                
Notes redemption price percentage of the principal amount           35.00%    
6.125% Senior Subordinated Notes due 2027 [Member] | Minimum [Member]                
Debt Instrument [Line Items]                
Indebtedness with outstanding balance under other agreements           $ 50,000,000    
5.0% Senior Subordinated Notes due 2023 [Member]                
Debt Instrument [Line Items]                
Principal amount       $ 300,000,000        
Stated interest rate on debt agreement       5.00%   5.00% 5.00%  
Notes maturity date       May 15, 2023        
Notes issued at a price of principal amount       100.00%        
Interest payable description           semi-annually in arrears on May 15 and November 15 of each year    
Notes redemption price percentage of the principal amount           100.00%    
Notes redemption price percentage of the par value due to change of control           101.00%    
Debt instrument maximum allowed dividends per share | $ / shares           $ 0.10    
Restrictive covenants under credit facilities and 6.125% notes           Specifically, the indenture governing the 5.0% Notes limits Sonic’s ability to pay quarterly cash dividends on Sonic’s Class A and Class B common stock in excess of $0.10 per share. Sonic may only pay quarterly cash dividends on Sonic’s Class A and Class B common stock if Sonic complies with the terms of the indenture governing the 5.0% Notes. Sonic was in compliance with all restrictive covenants in the indenture governing the 5.0% Notes as of December 31, 2017.    
Outstanding principal amount of the 6.125% notes           25.00%    
Outstanding notes repurchased amount             $ 10,700,000  
Repurchase amount paid in cash, plus accrued and unpaid interest related thereto             $ 10,600,000  
5.0% Senior Subordinated Notes due 2023 [Member] | Minimum [Member]                
Debt Instrument [Line Items]                
Indebtedness with outstanding balance under other agreements           $ 50,000,000    
9.0% Senior Subordinated Notes due 2018 [Member]                
Debt Instrument [Line Items]                
Stated interest rate on debt agreement       9.00%        
Convertible senior notes due       2018