The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Name:	us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Goodwill and Intangible Assets - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) store	Sep. 30, 2018 USD ($) store	Sep. 30, 2019 USD ($) store	Sep. 30, 2018 USD ($) store	Dec. 31, 2018 USD ($) store	Jun. 30, 2019 store	May 30, 2019 store	Jun. 30, 2018 store	Dec. 31, 2017 store
Goodwill And Intangible Assets [Line Items]
Impairment charges \| $			$ 0		$ 0
Number of owned and franchised locations \| store	1,899	1,646	1,899	1,646	1,742	1,859		1,608	1,518
Amortization of intangible assets \| $	$ 4,160,000	$ 4,027,000	$ 12,186,000	$ 12,052,000
Maine Acquisition
Goodwill And Intangible Assets [Line Items]
Number of owned and franchised locations \| store							4