Summary of Significant Accounting Policies - Recently Adopted Accounting Standards (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) item	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2017 USD ($)
Retained Earnings (Accumulated Deficit)	$ 478,348			$ 486,957
Increase in deferred tax assets	4,735			4,902
Additional paid-in capital	$ 260,305			$ 250,216
ASU 2016-09
Number of key accounting changes affect the timing of revenue recognition | item	2
Retained Earnings (Accumulated Deficit)					$ (600)
Increase in deferred tax assets					300
Additional paid-in capital					$ 900
ASU 2014-09
Retained Earnings (Accumulated Deficit)			$ (40)
Forecast | ASU 2016-02 | Minimum
Right-of-use asset		$ 80,000
Lease liability		100,000
Forecast | ASU 2016-02 | Maximum
Right-of-use asset		90,000
Lease liability		$ 110,000