Deferred Revenue of Membership Upgrade Sales and Deferred Commission Expense - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Movement in Deferred Revenue
Deferred revenue - upfront payments from membership upgrade sales as of December 31,	$ 116,363	$ 85,596
Cumulative effect of change in accounting principle				$ (15,186)
Membership upgrade sales current period, gross	19,111	15,191
Revenue recognized from membership upgrade sales upfront payments	(8,660)	(7,811)	$ (10,020)
Net increase in deferred revenue - upfront payments from membership grade sales	10,451	7,380
Deferred revenue - upfront payments from membership upgrade sales as of December 31,	126,814	116,363	85,596
Movement in Deferred Costs
Deferred commission expense, as of January 1,	40,308	31,443
Deferred commission expense	4,508	4,274
Commission expense recognized	(3,667)	(3,609)
Net increase in deferred commission expense	841	665
Deferred commission expense, as of December 31,	$ 41,149	$ 40,308	$ 31,443
Cumulative effect of change in accounting principle | Accounting Standards Update 2014-09 | Membership upgrade sales upfront payments, deferred, net
Movement in Deferred Revenue
Cumulative effect of change in accounting principle				23,387
Cumulative effect of change in accounting principle | Accounting Standards Update 2014-09 | Deferred Commission Expense
Movement in Deferred Revenue
Cumulative effect of change in accounting principle				$ 8,200