Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Receivables [Abstract]
Trade accounts receivable	$ 129,549		$ 140,209
Costs in excess of billings	22,214		11,610
Total accounts receivables	151,763		151,819
Less allowance for doubtful accounts	(6,581)		(6,434)
Accounts receivable	$ 145,182	$ 150,307	$ 145,385