Deferred Revenue-Entry of Right-to-Use Contracts and Deferred Commission Expense - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Movement in Deferred Revenue [Roll Forward]
Deferred revenue as of December 31,	$ 85,596	$ 81,484
Cumulative effect of change in accounting principle				$ (15,186)
Right-to-use contract upfront payments, deferred, net		14,132
Revenue recognized from right-to-use contract upfront payments	(7,811)	(10,020)	$ (9,248)
Right-to-use contract upfront payments, deferred, net	7,380	4,112
Deferred revenue—upfront payments from right-to-use contracts as of December 31,	116,363	85,596	81,484
Movement in Deferred Costs [Roll Forward]
Deferred commission expense, as of January 1,	31,443	31,375
Deferred commission expense	4,274	4,577
Commission expense recognized	3,609	4,509
Net increase in deferred commission expense	665	68
Deferred commission expense, as of December 31,	$ 40,308	$ 31,443	$ 31,375
Right-to-use contract upfront payments, deferred, net | Cumulative effect of change in accounting principle | Accounting Standards Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Cumulative effect of change in accounting principle				23,387
Deferred Commission Expense | Cumulative effect of change in accounting principle | Accounting Standards Update 2014-09
Movement in Deferred Revenue [Roll Forward]
Cumulative effect of change in accounting principle				$ 8,200