Balances Related to Intangible Assets (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 100,822	$ 101,139
Accumulated Amortization	(43,658)	(39,115)
Net Carrying Amount	57,164	62,024
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	92,946	93,235
Accumulated Amortization	(38,342)	(34,660)
Net Carrying Amount	$ 54,604	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	$ 5,929	5,954
Accumulated Amortization	(3,826)	(3,312)
Net Carrying Amount	$ 2,103	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	$ 1,888	1,890
Accumulated Amortization	(1,459)	(1,114)
Net Carrying Amount	$ 429	776
Other
Finite-Lived Intangible Assets [Line Items]
Estimated Useful Life in Years	20 years
Gross Carrying Amount	$ 59	60
Accumulated Amortization	(31)	(29)
Net Carrying Amount	$ 28	$ 31