Summary of Significant Accounting Policies - Schedule of Annual Dues Deferred Revenue (Detail) - Annual Dues - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Revenue Arrangement [Line Items]
Deferred revenue recognition period	12 months
Balance at beginning of period	$ 12,912	$ 12,344	$ 11,599
New billings	31,952	31,294	30,269
Revenue recognized	(31,758)	(30,726)	(29,524)
Balance at end of period	$ 13,106	$ 12,912	$ 12,344