| Fair Value Measurements (Tables) | 6 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Jun. 30, 2015 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fair Value Disclosures [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Assets and Liabilities Recorded at Fair Value | Assets and liabilities recorded at fair value in the accompanying condensed consolidated balance sheets as of June 30, 2015 and December 31, 2014 are as follows: 
 
 
 (1) Included in other assets in the accompanying condensed consolidated balance sheets. (2) As of June 30, 2015, approximately $5.1 million and $4.6 million were included in other accrued liabilities and other long-term liabilities, respectively, in the accompanying condensed consolidated balance sheets. As of December 31, 2014, approximately $7.5 million and $2.8 million were included in other accrued liabilities and other long-term liabilities, respectively, in the accompanying condensed consolidated balance sheets. (3) As of June 30, 2015, approximately $0.6 million was included in both other accrued liabilities and other long-term liabilities in the accompanying condensed consolidated balance sheets. As of December 31, 2014, approximately $0.7 million and $0.8 million were included in other accrued liabilities and other long-term liabilities, respectively, in the accompanying condensed consolidated balance sheets. (4) Included in other long-term liabilities in the accompanying condensed consolidated balance sheets. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fair Value and Carrying Value of Fixed Rate Long-Term Debt | At June 30, 2015 and December 31, 2014, the fair value and carrying value of Sonic’s fixed rate long-term debt were as follows: 
 
 
 (1) As determined by market quotations as of June 30, 2015 and December 31, 2014, respectively (Level 1). (1) As determined by discounted cash flows (Level 3) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||