Revenue Recognition - Contract Balances with Contract Customers (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts receivable, net	$ 505	$ 476
Costs and estimated earnings in excess of billings on uncompleted contracts	0	987
Other current assets	574	1,311
Contract liabilities	10,028	10,000
Billings on uncompleted contracts in excess of related costs	10,000	0
Other current liabilities	8	10,154
Contracts with Customers
Accounts receivable, net	505	476
Costs and estimated earnings in excess of billings on uncompleted contracts	0	987
Deferred revenue	28	0
Contract liabilities	10,000	0
Other current liabilities	$ 0	$ 10,000