Revenue Recognition - Contract Balances with Contract Customers (details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts receivable	$ 2,502	$ 15
Costs and estimated earnings in excess of billings on uncompleted contracts	258	680
Other current assets	1,547	1,015
Billings on uncompleted contracts in excess of related costs	4	5
Other current liabilities	10,103	10,142
Contracts with Customers
Accounts receivable	2,502	15
Costs and estimated earnings in excess of billings on uncompleted contracts	258	680
Other current assets	11	70
Billings on uncompleted contracts in excess of related costs	4	5
Other current liabilities	$ 10,000	$ 10,000