Revenue - Significant Changes in Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change In Contract With Customer, Liability [Roll Forward]
Contract liabilities balance, beginning of year	$ 28,866	$ 42,809	$ 56,426
Revenue recognized	(28,414)	(15,247)	(13,493)
Increase due to cash received, excluding amounts recognized as revenue during the period	1,188	1,304	(124)
Contract liabilities balance, end of year	$ 1,640	$ 28,866	$ 42,809