Supplemental Disclosure to Cash Flows - Summary of Supplemental Non-Cash and Other Cash Flow Information (Detail) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 349,462	$ 75,105	$ 40,651
Restricted Cash	1,565	3,333	3,317
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	351,027	78,438	43,968	$ 59,526
Cash paid for income taxes, net of refunds	10,609	11,487	14,048
Non-cash transactions:
Contingent consideration related to business combinations	0	1,007	3,325
Property and equipment purchases in accounts payable	$ 501	$ 133	$ 82
Non-cash purchase consideration related to business combinations	12,508	0	0
Purchase of assets under capital lease obligations	$ 0	$ 0	$ 134