Goodwill and Intangibles - Intangible Assets and Accumulated Amortization Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 193,328	$ 161,118
Accumulated Amortization	(101,935)	(92,027)
Net Carrying Amount	91,393	69,091
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	145,362	135,927
Accumulated Amortization	(95,690)	(86,342)
Net Carrying Amount	49,672	49,585
Developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,783	2,893
Accumulated Amortization	(2,783)	(2,893)
Net Carrying Amount	0	0
Other
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	45,183	22,298
Accumulated Amortization	(3,462)	(2,792)
Net Carrying Amount	$ 41,721	$ 19,506