Supplemental Disclosure to Cash Flows - Summary of Supplemental Non-Cash and Other Cash Flow Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Cash paid for income taxes, net of refunds	$ 11,487	$ 14,048	$ 6,759
Non-cash transactions:
Contingent consideration related to business combinations	1,007	3,325	952
Property and equipment purchases in accounts payable	133	82	315
Purchase of assets under capital lease obligations	$ 0	$ 134	$ 0