Deferred Revenue-Entry of Right-to-Use Contracts and Deferred Commission Expense - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Deferred Revenue [Roll Forward]
Deferred revenue—upfront payments from right-to-use contracts, as of January 1,	$ 74,174	$ 68,673
Right-to-use contracts current period, gross	12,783	13,892	$ 13,815
Revenue recognized from right-to-use contract upfront payments	(8,552)	(8,391)	(8,121)
Right-to-use contract upfront payments, deferred, net	4,231	5,501
Deferred revenue—upfront payments from right-to-use contracts, as of December 31,	78,405	74,174	68,673
Movement in Deferred Costs [Roll Forward]
Deferred commission expense, as of January 1,	28,589	25,251
Deferred commission expense	5,871	6,272
Commission expense recognized	(3,595)	(2,934)	(2,601)
Net increase in deferred commission expense	2,276	3,338
Deferred commission expense, as of December 31,	$ 30,865	$ 28,589	$ 25,251