Deferred Revenue-Right-to-use contracts and Deferred commission expense - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Movement in Deferred Revenue [Roll Forward]
Deferred revenue - right-to-use contracts, beginning balance	$ 78,405	$ 74,174
Right-to-use contracts current period, gross	2,532	2,797
Revenue recognized from right-to-use contract upfront payments	(2,230)	(2,024)
Right-to-use contract upfront payments, deferred, net	302	773
Deferred revenue - right-to-use contracts, ending balance	78,707	74,947
Movement in Deferred Costs [Roll Forward]
Deferred commission expense, beginning balance	30,865	28,589
Deferred commission expense	895	1,142
Commission expense recognized	(1,002)	(829)
Net (decrease) increase in deferred commission expense	(107)	313
Deferred commission expense, ending balance	$ 30,758	$ 28,902