Deferred Revenue-Right-to-use contracts and Deferred commission expense - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 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	5,618	6,375
Revenue recognized from right-to-use contract upfront payments	(4,518)	(4,147)
Right-to-use contract upfront payments, deferred, net	1,100	2,228
Deferred revenue - right-to-use contracts, ending balance	79,505	76,402
Movement in Deferred Costs [Roll Forward]
Deferred commission expense, beginning balance	30,865	28,589
Deferred commission expense	2,238	3,067
Commission expense recognized	(2,019)	(1,696)
Net increase in deferred commission expense	219	1,371
Deferred commission expense, ending balance	$ 31,084	$ 29,960