Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 27,964	$ 39,924	$ 27,964	$ 39,924
Deferred tax liability	8,945		8,945		$ 3,372
Amortization of commissions assets			1,200
Revenue recognized	74,200	$ 62,915	278,889
Unbilled contracts	$ 91,879		91,879
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings						$ 2,711
Commission asset balance						3,500
Deferred tax liability						$ 800
Subscription Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognized			$ 141,300	$ 112,700