Income Taxes (Tables)
   | 
12 Months Ended | 
Dec. 31, 2016  | 
| Income Tax Disclosure [Abstract] | 
 
 | 
| Provision for Income Taxes for Continuing Operations - (Benefit) Expense | 
The provision for income taxes for continuing operations - (benefit) expense consists of the following:  
  
| 
   
 | 
   
 | 
 Year Ended December 31, 
 | 
   
 | 
 
| 
   
 | 
   
 | 
 2016 
 | 
   
 | 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
 
| 
   
 | 
   
 | 
 (In thousands) 
 | 
   
 | 
 
| 
 Current: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Federal 
 | 
   
 | 
 $ 
 | 
 43,655 
 | 
   
 | 
   
 | 
 $ 
 | 
 36,241 
 | 
   
 | 
   
 | 
 $ 
 | 
 36,874 
 | 
   
 | 
 
| 
 State 
 | 
   
 | 
   
 | 
 3,766 
 | 
   
 | 
   
 | 
   
 | 
 6,414 
 | 
   
 | 
   
 | 
   
 | 
 5,771 
 | 
   
 | 
 
| 
 Total current 
 | 
   
 | 
   
 | 
 47,421 
 | 
   
 | 
   
 | 
   
 | 
 42,655 
 | 
   
 | 
   
 | 
   
 | 
 42,645 
 | 
   
 | 
 
| 
 Deferred 
 | 
   
 | 
   
 | 
 13,275 
 | 
   
 | 
   
 | 
   
 | 
 14,410 
 | 
   
 | 
   
 | 
   
 | 
 20,523 
 | 
   
 | 
 
| 
 Total provision for income taxes for continuing operations - (benefit) expense 
 | 
   
 | 
 $ 
 | 
 60,696 
 | 
   
 | 
   
 | 
 $ 
 | 
 57,065 
 | 
   
 | 
   
 | 
 $ 
 | 
 63,168 
 | 
   
 | 
 
 
 
  
 
 | 
| Reconciliation of Statutory Federal Income Tax Rate with Federal and State Overall Effective Income Tax Rate from Continuing Operations | 
The reconciliation of the statutory federal income tax rate with Sonic’s federal and state overall effective income tax rate from continuing operations is as follows:  
  
| 
   
 | 
   
 | 
 Year Ended December 31, 
 | 
   
 | 
 
| 
   
 | 
   
 | 
 2016 
 | 
   
 | 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
 
| 
 Statutory federal income tax rate 
 | 
   
 | 
   
 | 
 35.00 
 | 
 % 
 | 
   
 | 
   
 | 
 35.00 
 | 
 % 
 | 
   
 | 
   
 | 
 35.00 
 | 
 % 
 | 
 
| 
 Effective state income tax rate 
 | 
   
 | 
   
 | 
 2.04 
 | 
 % 
 | 
   
 | 
   
 | 
 3.26 
 | 
 % 
 | 
   
 | 
   
 | 
 3.15 
 | 
 % 
 | 
 
| 
 Valuation allowance adjustments 
 | 
   
 | 
   
 | 
 0.85 
 | 
 % 
 | 
   
 | 
   
 | 
 (0.45 
 | 
 %) 
 | 
   
 | 
   
 | 
 (0.14 
 | 
 %) 
 | 
 
| 
 Uncertain tax positions 
 | 
   
 | 
   
 | 
 0.17 
 | 
 % 
 | 
   
 | 
   
 | 
 (0.14 
 | 
 %) 
 | 
   
 | 
   
 | 
 (0.08 
 | 
 %) 
 | 
 
| 
 Other 
 | 
   
 | 
   
 | 
 1.05 
 | 
 % 
 | 
   
 | 
   
 | 
 1.64 
 | 
 % 
 | 
   
 | 
   
 | 
 1.13 
 | 
 % 
 | 
 
| 
 Effective income tax rate 
 | 
   
 | 
   
 | 
 39.11 
 | 
 % 
 | 
   
 | 
   
 | 
 39.31 
 | 
 % 
 | 
   
 | 
   
 | 
 39.06 
 | 
 % 
 | 
 
 
 
  
 
 | 
| Components of Deferred Tax Assets and Liabilities | 
Significant components of Sonic’s deferred tax assets and liabilities are as follows: 
  
| 
   
 | 
   
 | 
 December 31, 2016 
 | 
   
 | 
   
 | 
 December 31, 2015 
 | 
   
 | 
 
| 
   
 | 
   
 | 
 (In thousands) 
 | 
   
 | 
 
| 
 Deferred tax assets: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Accruals and reserves 
 | 
   
 | 
 $ 
 | 
 34,884 
 | 
   
 | 
   
 | 
 $ 
 | 
 33,397 
 | 
   
 | 
 
| 
 State net operating loss carryforwards 
 | 
   
 | 
   
 | 
 10,777 
 | 
   
 | 
   
 | 
   
 | 
 10,187 
 | 
   
 | 
 
| 
 Fair value of interest rate swaps 
 | 
   
 | 
   
 | 
 1,406 
 | 
   
 | 
   
 | 
   
 | 
 3,793 
 | 
   
 | 
 
| 
 Interest and state taxes associated with the liability for uncertain income tax positions 
 | 
   
 | 
   
 | 
 1,746 
 | 
   
 | 
   
 | 
   
 | 
 1,725 
 | 
   
 | 
 
| 
 Other 
 | 
   
 | 
   
 | 
 774 
 | 
   
 | 
   
 | 
   
 | 
 864 
 | 
   
 | 
 
| 
 Total deferred tax assets 
 | 
   
 | 
   
 | 
 49,587 
 | 
   
 | 
   
 | 
   
 | 
 49,966 
 | 
   
 | 
 
| 
 Deferred tax liabilities: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Basis difference in inventory 
 | 
   
 | 
   
 | 
 (1,506 
 | 
 ) 
 | 
   
 | 
   
 | 
 (1,530 
 | 
 ) 
 | 
 
| 
 Basis difference in property and equipment 
 | 
   
 | 
   
 | 
 (9,335 
 | 
 ) 
 | 
   
 | 
   
 | 
 (9,850 
 | 
 ) 
 | 
 
| 
 Basis difference in goodwill 
 | 
   
 | 
   
 | 
 (101,999 
 | 
 ) 
 | 
   
 | 
   
 | 
 (86,504 
 | 
 ) 
 | 
 
| 
 Other 
 | 
   
 | 
   
 | 
 (3,540 
 | 
 ) 
 | 
   
 | 
   
 | 
 (3,249 
 | 
 ) 
 | 
 
| 
 Total deferred tax liability 
 | 
   
 | 
   
 | 
 (116,380 
 | 
 ) 
 | 
   
 | 
   
 | 
 (101,133 
 | 
 ) 
 | 
 
| 
 Valuation allowance 
 | 
   
 | 
   
 | 
 (7,211 
 | 
 ) 
 | 
   
 | 
   
 | 
 (5,880 
 | 
 ) 
 | 
 
| 
 Net deferred tax asset (liability) 
 | 
   
 | 
 $ 
 | 
 (74,004 
 | 
 ) 
 | 
   
 | 
 $ 
 | 
 (57,047 
 | 
 ) 
 | 
 
 
 
  
 
 | 
| Summary of Changes in Liability Related to Unrecognized Tax Benefits | 
A summary of the changes in the liability related to Sonic’s unrecognized tax benefits is presented below. 
  
| 
   
 | 
   
 | 
 2016 
 | 
   
 | 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
 
| 
   
 | 
   
 | 
 (In thousands) 
 | 
   
 | 
 
| 
 Unrecognized tax benefit liability, January 1 (1) 
 | 
   
 | 
 $ 
 | 
 4,755 
 | 
   
 | 
   
 | 
 $ 
 | 
 5,740 
 | 
   
 | 
   
 | 
 $ 
 | 
 6,693 
 | 
   
 | 
 
| 
 Prior period positions: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Increases 
 | 
   
 | 
   
 | 
 939 
 | 
   
 | 
   
 | 
   
 | 
 175 
 | 
   
 | 
   
 | 
   
 | 
 181 
 | 
   
 | 
 
| 
 Decreases 
 | 
   
 | 
   
 | 
 (415 
 | 
 ) 
 | 
   
 | 
   
 | 
 - 
 | 
   
 | 
   
 | 
   
 | 
 (66 
 | 
 ) 
 | 
 
| 
 Increases from current period positions 
 | 
   
 | 
   
 | 
 615 
 | 
   
 | 
   
 | 
   
 | 
 184 
 | 
   
 | 
   
 | 
   
 | 
 195 
 | 
   
 | 
 
| 
 Settlements 
 | 
   
 | 
   
 | 
 - 
 | 
   
 | 
   
 | 
   
 | 
 - 
 | 
   
 | 
   
 | 
   
 | 
 (897 
 | 
 ) 
 | 
 
| 
 Lapse of statute of limitations 
 | 
   
 | 
   
 | 
 (1,290 
 | 
 ) 
 | 
   
 | 
   
 | 
 (1,114 
 | 
 ) 
 | 
   
 | 
   
 | 
 (170 
 | 
 ) 
 | 
 
| 
 Other 
 | 
   
 | 
   
 | 
 (247 
 | 
 ) 
 | 
   
 | 
   
 | 
 (230 
 | 
 ) 
 | 
   
 | 
   
 | 
 (196 
 | 
 ) 
 | 
 
| 
 Unrecognized tax benefit liability, December 31 (2) 
 | 
   
 | 
 $ 
 | 
 4,357 
 | 
   
 | 
   
 | 
 $ 
 | 
 4,755 
 | 
   
 | 
   
 | 
 $ 
 | 
 5,740 
 | 
   
 | 
 
 
 
| 
 (1) 
 | 
 Excludes accrued interest and penalties of $1.1 million, $1.2 million and $1.1 million at January 1, 2016, 2015 and 2014, respectively.  
 | 
 
 
 
| 
 (2) 
 | 
 Excludes accrued interest and penalties of $0.8 million, $1.1 million and $1.2 million at December 31, 2016, 2015 and 2014, respectively. Amount presented is net of state net operating losses of $0.3 million, $0.6 million and $0.8 million at December 31, 2016, 2015 and 2014, respectively.  
 | 
 
 
 
 
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