Business Combinations - Summary of Business Acquisitions (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Business Acquisition [Line Items]
Cash paid	$ 11,505	$ 107,212
Seller Obligations	3,093	2,302
Fair Value of Common Stock Issued		10,859
Total Purchase Price	14,598	120,373
Revenue	301,728	255,669
Net Income (Loss)	$ 6,394	$ 6,364
CDG Acquisition [Member]
Business Acquisition [Line Items]
Date	Mar. 19, 2018
Acquisition Type	Asset
Cash paid	$ 9,440
Seller Obligations	1,973
Total Purchase Price	11,413
Revenue	400
Net Income (Loss)	$ (15)
Other Acquisition [Member]
Business Acquisition [Line Items]
Date	Jan. 15, 2018	Mar. 20, 2017
Acquisition Type	Asset	Asset
Cash paid	$ 2,065	$ 3,402
Seller Obligations	1,120	300
Total Purchase Price	3,185	3,702
Revenue	1,271	518
Net Income (Loss)	66	$ 21
2018 Acquisitions [Member]
Business Acquisition [Line Items]
Revenue	1,671
Net Income (Loss)	51
Alpha [Member]
Business Acquisition [Line Items]
Date		Jan. 05, 2017
Acquisition Type		Share
Cash paid		$ 103,810
Seller Obligations		2,002
Fair Value of Common Stock Issued	$ 10,900	10,859
Total Purchase Price		116,671
Revenue		28,166
Net Income (Loss)		900
2017 Acquisitions [Member]
Business Acquisition [Line Items]
Revenue		28,684
Net Income (Loss)		$ 921