Goodwill and Other Intangible Assets - Schedule of Activity in Goodwill and Intangible Assets, Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible assets, net
Balance, beginning of period	$ 38,427	$ 40,887	$ 41,783
Acquisition	275,700	0	2,400
Amortization expense	(12,173)	(2,460)	(3,296)
Balance, end of period	301,954	38,427	40,887
Goodwill
Balance, beginning of period	6,788	6,701	5,260
Acquisition	163,365	0	1,441
Acquisition related adjustments	0	87	0
Balance, end of period	$ 170,153	$ 6,788	$ 6,701