Deferred Revenue - Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Deferred Revenue
Beginning balance	$ 280,291	$ 250,534	$ 284,253	$ 273,241
Billings for the period	130,945	90,780	241,671	160,227
Revenue recognized	(113,910)	(97,230)	(228,598)	(189,384)
Ending balance	$ 297,326	$ 244,084	$ 297,326	$ 244,084