Deferred Revenue-Right-to-use contracts and Deferred commission expense - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 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	9,290	10,264
Revenue recognized from right-to-use contract upfront payments	(6,863)	(6,335)
Right-to-use contract upfront payments, deferred, net	2,427	3,929
Deferred revenue - right-to-use contracts, ending balance	80,832	78,103
Movement in Deferred Costs [Roll Forward]
Deferred commission expense, beginning balance	30,865	28,589
Deferred commission expense	3,641	4,821
Commission expense recognized	(3,071)	(2,629)
Net increase in deferred commission expense	570	2,192
Deferred commission expense, ending balance	$ 31,435	$ 30,781