Business Information - Geographical Distribution of Revenues and Assets (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Revenues	$ 173,496	$ 121,346	$ 89,284	$ 115,304	$ 103,822	$ 147,322	$ 72,469	$ 82,325	$ 499,430	$ 405,938	$ 401,069
Assets
Assets	590,476				467,252				590,476	467,252
Domestic
Revenues
Revenues									465,046	381,389	352,391
Assets
Assets	545,049				444,040				545,049	444,040
International
Revenues
Revenues									34,384	24,549	$ 48,678
Assets
Assets	$ 45,427				$ 23,212				$ 45,427	$ 23,212