Revenue - Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction
Deferred revenue	$ 36,614	$ 29,745	$ 29,055
Deferred revenue on consolidated balance sheet	$ 19,700	$ 26,300
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	1 year
Remaining unearned revenue	$ 15,400
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction
Revenue recognized over remaining contract term
Remaining unearned revenue	$ 21,200