Revenue - Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction
Deferred revenue	$ 29,745	$ 29,055	$ 23,441
Deferred revenue on consolidated balance sheet	$ 26,300	$ 19,600
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction
Revenue recognized over remaining contract term	1 year
Remaining unearned revenue	$ 15,800
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction
Revenue recognized over remaining contract term
Remaining unearned revenue	$ 13,900