Revenue Recognition - Contract Balances with Contract Customers (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts receivable, net	$ 0	$ 1,079
Accrued liabilities	0	432
Deferred revenue	0	21
Contract liabilities	7,765	9,755
Other current liabilities	0	83
Other current assets	698	729
Contracts with Customers
Accounts receivable, net	0	1,079
Accrued liabilities	0	432
Deferred revenue	0	21
Contract liabilities	$ 7,765	$ 9,755