Goodwill and Intangible Assets - Summary of Intangible Assets of Company by Major Class (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Schedule Of Intangible Assets [Line Items]
Intangible assets subject to amortization, Gross Carrying Amount	$ 156,049	$ 156,535
Intangible assets subject to amortization, Accumulated Amortization	(87,502)	(83,094)
Intangible assets subject to amortization, Net Carrying Amount	68,547	73,441
Customer relationships and other intangibles [Member]
Schedule Of Intangible Assets [Line Items]
Intangible assets subject to amortization, Gross Carrying Amount	137,672	138,110
Intangible assets subject to amortization, Accumulated Amortization	(76,333)	(72,192)
Intangible assets subject to amortization, Net Carrying Amount	$ 61,339	$ 65,918
Intangible assets subject to amortization, Weighted Average Useful Life (years)	16 years	16 years
Non-compete Agreements [Member]
Schedule Of Intangible Assets [Line Items]
Intangible assets subject to amortization, Gross Carrying Amount	$ 4,652	$ 4,659
Intangible assets subject to amortization, Accumulated Amortization	(4,260)	(4,260)
Intangible assets subject to amortization, Net Carrying Amount	$ 392	$ 399
Intangible assets subject to amortization, Weighted Average Useful Life (years)	4 years	4 years
Trademarks [Member]
Schedule Of Intangible Assets [Line Items]
Intangible assets subject to amortization, Gross Carrying Amount	$ 13,725	$ 13,766
Intangible assets subject to amortization, Accumulated Amortization	(6,909)	(6,642)
Intangible assets subject to amortization, Net Carrying Amount	$ 6,816	$ 7,124
Intangible assets subject to amortization, Weighted Average Useful Life (years)	14 years	14 years