Recent and Pending Accounting Standards (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 194,527	$ 191,796
Decrease to deferred revenue	(31,600)	(32,500)
Decrease to accumulated other comprehensive income	1,508	1,088
Accounting Standards Update 2014-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		6,400
Decrease to deferred revenue	$ 4,200	4,200
Decrease to accumulated other comprehensive income		200
Unbilled receivables		1,300
Prepaid commissions		$ 700