Balances Related to Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 101,480	$ 101,139
Accumulated Amortization	(41,038)	(39,115)
Net Carrying Amount	60,442	62,024
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	93,547	93,235
Accumulated Amortization	(36,259)	(34,660)
Net Carrying Amount	$ 57,288	58,575
Customer relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	15 years
Customer relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	20 years
Trade names/trademarks
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 5,983	5,954
Accumulated Amortization	(3,473)	(3,312)
Net Carrying Amount	$ 2,510	2,642
Trade names/trademarks | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	5 years
Trade names/trademarks | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	10 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	5 years
Gross Carrying Amount	$ 1,890	1,890
Accumulated Amortization	(1,276)	(1,114)
Net Carrying Amount	$ 614	776
Other
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	20 years
Gross Carrying Amount	$ 60	60
Accumulated Amortization	(30)	(29)
Net Carrying Amount	$ 30	$ 31