Revenue Information and Deferred Sales Commissions - Schedule of Cumulative Effects of Changes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Assets
Other current assets	$ 4,532		$ 4,469	$ 1,145
Other assets	4,504		4,353	1,391
Liabilities
Accounts payable	18,018		18,876	18,620
Accrued expenses and other liabilities	12,810		12,897	12,790
Stockholders’ Equity
Accumulated deficit	(354,216)		(345,161)	(351,084)
Revenues	81,061	$ 75,757
Sales and marketing	48,418	42,182
Net loss	(9,055)	$ (6,795)
Balances Without Adoption of New Revenue Standard
Assets
Other current assets				1,145
Other assets				1,391
Liabilities
Accounts payable				18,620
Accrued expenses and other liabilities				12,790
Stockholders’ Equity
Accumulated deficit				$ (351,084)
ASU 2014-09 | Balances Without Adoption of New Revenue Standard
Assets
Other current assets	789
Other assets	1,358
Liabilities
Accounts payable	17,581
Accrued expenses and other liabilities	12,586
Stockholders’ Equity
Accumulated deficit	(360,444)
Revenues	80,758
Sales and marketing	48,420
Net loss	(9,360)
ASU 2014-09 | Adjustments Due to Adoption of New Revenue Standard
Assets
Other current assets	3,743		3,324
Other assets	3,146		2,962
Liabilities
Accounts payable	437		256
Accrued expenses and other liabilities	224		107
Stockholders’ Equity
Accumulated deficit	6,228		$ 5,923
Revenues	303
Sales and marketing	(2)
Net loss	$ (305)