Revenue Recognition - Changes in Balance of Deferred Revenues (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)
Revenue Recognition
Balance	$ 72,930
Increase in deferred revenues	1,030
Refunds of revenues previously deferred	(10,000)
Revenue recognized during the period that was included in deferred revenues at the beginning of the period	(30,292)
Revenue recognized from performance obligations satisfied within the same period	(783)
Balance	$ 32,885