Related Parties - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Notes Receivable Related Parties [Line Items]
Lease paid by company	$ 38,000	$ 38,400	$ 37,000
Revenue	922,003	855,340	799,832
Director [Member]
Notes Receivable Related Parties [Line Items]
Lease paid by company	3,000	3,300	3,200
Akin Gump [Member]
Notes Receivable Related Parties [Line Items]
Legal charges paid	200	200	100
CPA Firms [Member]
Notes Receivable Related Parties [Line Items]
Revenue	$ 154,000	$ 156,400	$ 144,800

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration