Business Combinations, Goodwill and Intangible Assets - Summary of Company's Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 108,884	$ 99,487
Accumulated Amortization	(60,826)	(46,617)
Total	48,058	52,870
Intangible assets, gross	109,784	100,387
Intangible assets, net	48,958	53,770
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	82,165	75,181
Accumulated Amortization	(43,667)	(32,968)
Total	38,498	42,213
Leasehold benefits
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	2,888	2,715
Accumulated Amortization	(2,596)	(2,247)
Total	292	468
Developed technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	15,835	14,186
Accumulated Amortization	(8,749)	(6,468)
Total	7,086	7,718
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	2,045	2,045
Accumulated Amortization	(1,780)	(1,612)
Total	265	433
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	5,951	5,360
Accumulated Amortization	(4,034)	(3,322)
Total	1,917	2,038
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets, trade names and trademarks	$ 900	$ 900