Commitments and Contingencies	12 Months Ended
Aug. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Payment Card Breach On September 18, 2017, the Company was informed by its payment card processor that there appeared to be suspicious activity involving credit and debit cards used at certain Sonic Drive-In locations. Upon learning of the suspicious activity, the Company immediately contacted and began working with law enforcement to investigate the matter. At the same time, the Company immediately launched its own investigation with the help of experienced third-party forensics firms. On October 4, 2017, the Company issued a public statement notifying guests and the public that it had discovered that credit and debit card numbers may have been acquired without authorization as part of a malware attack experienced at certain Sonic Drive-In locations. Subsequent to September 18, 2017, the Company incurred costs associated with this payment card breach, including legal fees, investigative fees and costs of communications with customers. In addition, payment card companies may issue assessments for card replacement and card issuer losses alleged to be associated with the payment card breach, as well as fines and penalties relating to the payment card breach. The Company expects that certain of such costs and assessments will be covered under the Company’s cyber liability insurance coverage. Currently, the Company cannot reasonably estimate a loss or range of losses associated with resolution of the payment card networks’ expected claims for non-ordinary course operating expenses or any amounts associated with the networks’ expected claims for alleged card issuer losses and/or card replacement costs. The Company believes that it is possible that the ultimate amount to be paid on payment card network claims, to the extent not covered by, or in excess of the limits of, the Company’s cyber liability insurance, could be material to its results of operations in future periods. The Company will continue to evaluate information as it becomes known and will record an estimate for losses at the time or times when it is both probable that a loss has been incurred and the amount of the loss is reasonably estimable. In addition, the Company may incur legal and other professional services expenses associated with the payment card breach in future periods. The Company will recognize these expenses as such services are received. Litigation The Company was named as a defendant in nine purported class action complaints related to the 2017 payment card breach at certain Sonic Drive-Ins. The cases were consolidated in the Northern District of Ohio (the “Litigation”). The plaintiffs in the Litigation assert various claims related to the Company’s alleged failure to safeguard customer credit card information and seek monetary damages, injunctive and declaratory relief and attorneys’ fees and costs. The Company believes it has meritorious defenses to the Litigation and intends to vigorously oppose the claims asserted by the plaintiffs. On October 10, 2018, the parties to the Litigation filed a joint motion seeking preliminary approval of a class settlement. Based on the terms of class settlement, which is subject to final court approval, we do not believe any payments made in connection with the class settlement or the Litigation more generally would be in excess of our cyber liability insurance coverage. The estimated settlement amount has been recorded in accrued liabilities, with an offsetting amount recorded in accounts and notes receivable, net, related to the cyber liability insurance coverage. The Company has since been named as a defendant in one additional purported class action complaint filed on October 16, 2018, in the United States District Court for the Eastern District of Arkansas. We cannot provide assurance that we will not become subject to other inquiries or claims relating to the payment card breach in the future. Although we maintain cyber liability insurance, it is possible the ultimate amount paid by us relating to the payment card breach may be in excess of our cyber liability insurance coverage applicable to claims of this nature. We are unable to estimate the amount of any such excess. The Company is involved in various other legal proceedings and has certain unresolved claims pending. Based on the information currently available, management believes that all claims currently pending are either covered by insurance or would not have a material adverse effect on the Company’s business, operating results or financial condition. Note Repurchase Agreement On December 20, 2013, the Company extended a note purchase agreement to a bank that serves to guarantee the repayment of a franchisee loan, with a term through 2018, and also benefits the franchisee with a lower financing rate. In the event of default by the franchisee, the Company would purchase the franchisee loan from the bank, thereby becoming the note holder and providing an avenue of recourse with the franchisee. The Company recorded a liability for this guarantee which was based on the Company’s estimate of fair value. As of August 31, 2018, the balance of the franchisee’s loan was $4.4 million. Lease Commitments The Company has obligations under various operating lease agreements with third-party lessors related to the real estate for certain Company Drive-In operations that were sold to franchisees. Under these agreements, which expire through 2029, the Company remains secondarily liable for the lease payments for which it was responsible as the original lessee. As of August 31, 2018, the amount remaining under these guaranteed lease obligations totaled $15.1 million. At this time, the Company does not anticipate any material defaults under the foregoing leases; therefore, no liability has been provided. Purchase Obligations At August 31, 2018, the Company had purchase obligations of approximately $113.2 million which primarily related to its estimated share of system commitments for food products. The Company has excluded agreements that are cancelable without penalty.

Commitments and Contingencies

Payment Card Breach

On September 18, 2017, the Company was informed by its payment card processor that there appeared to be suspicious activity involving credit and debit cards used at certain Sonic Drive-In locations. Upon learning of the suspicious activity, the Company immediately contacted and began working with law enforcement to investigate the matter. At the same time, the Company immediately launched its own investigation with the help of experienced third-party forensics firms. On October 4, 2017, the Company issued a public statement notifying guests and the public that it had discovered that credit and debit card numbers may have been acquired without authorization as part of a malware attack experienced at certain Sonic Drive-In locations.

Subsequent to September 18, 2017, the Company incurred costs associated with this payment card breach, including legal fees, investigative fees and costs of communications with customers. In addition, payment card companies may issue assessments for card replacement and card issuer losses alleged to be associated with the payment card breach, as well as fines and penalties relating to the payment card breach. The Company expects that certain of such costs and assessments will be covered under the Company’s cyber liability insurance coverage.

Currently, the Company cannot reasonably estimate a loss or range of losses associated with resolution of the payment card networks’ expected claims for non-ordinary course operating expenses or any amounts associated with the networks’ expected claims for alleged card issuer losses and/or card replacement costs. The Company believes that it is possible that the ultimate amount to be paid on payment card network claims, to the extent not covered by, or in excess of the limits of, the Company’s cyber liability insurance, could be material to its results of operations in future periods. The Company will continue to evaluate information as it becomes known and will record an estimate for losses at the time or times when it is both probable that a loss has been incurred and the amount of the loss is reasonably estimable.

In addition, the Company may incur legal and other professional services expenses associated with the payment card breach in future periods. The Company will recognize these expenses as such services are received.

Litigation

The Company was named as a defendant in nine purported class action complaints related to the 2017 payment card breach at certain Sonic Drive-Ins. The cases were consolidated in the Northern District of Ohio (the “Litigation”). The plaintiffs in the Litigation assert various claims related to the Company’s alleged failure to safeguard customer credit card information and seek monetary damages, injunctive and declaratory relief and attorneys’ fees and costs. The Company believes it has meritorious defenses to the Litigation and intends to vigorously oppose the claims asserted by the plaintiffs. On October 10, 2018, the parties to the Litigation filed a joint motion seeking preliminary approval of a class settlement. Based on the terms of class settlement, which is subject to final court approval, we do not believe any payments made in connection with the class settlement or the Litigation more generally would be in excess of our cyber liability insurance coverage. The estimated settlement amount has been recorded in accrued liabilities, with an offsetting amount recorded in accounts and notes receivable, net, related to the cyber liability insurance coverage. The Company has since been named as a defendant in one additional purported class action complaint filed on October 16, 2018, in the United States District Court for the Eastern District of Arkansas. We cannot provide assurance that we will not become subject to other inquiries or claims relating to the payment card breach in the future. Although we maintain cyber liability insurance, it is possible the ultimate amount paid by us relating to the payment card breach may be in excess of our cyber liability insurance coverage applicable to claims of this nature. We are unable to estimate the amount of any such excess.

The Company is involved in various other legal proceedings and has certain unresolved claims pending. Based on the information currently available, management believes that all claims currently pending are either covered by insurance or would not have a material adverse effect on the Company’s business, operating results or financial condition.

Note Repurchase Agreement

On December 20, 2013, the Company extended a note purchase agreement to a bank that serves to guarantee the repayment of a franchisee loan, with a term through 2018, and also benefits the franchisee with a lower financing rate. In the event of default by the franchisee, the Company would purchase the franchisee loan from the bank, thereby becoming the note holder and providing an avenue of recourse with the franchisee. The Company recorded a liability for this guarantee which was based on the Company’s estimate of fair value. As of August 31, 2018, the balance of the franchisee’s loan was $4.4 million.

Lease Commitments

The Company has obligations under various operating lease agreements with third-party lessors related to the real estate for certain Company Drive-In operations that were sold to franchisees. Under these agreements, which expire through 2029, the Company remains secondarily liable for the lease payments for which it was responsible as the original lessee. As of August 31, 2018, the amount remaining under these guaranteed lease obligations totaled $15.1 million. At this time, the Company does not anticipate any material defaults under the foregoing leases; therefore, no liability has been provided.

Purchase Obligations

At August 31, 2018, the Company had purchase obligations of approximately $113.2 million which primarily related to its estimated share of system commitments for food products. The Company has excluded agreements that are cancelable without penalty.