Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Receivables [Abstract]
Trade accounts receivable	$ 81,193	$ 102,277
Contract receivables:
Amounts billed	41,569	53,830
Costs in excess of billings	6,582	13,730
Total contract receivables	48,151	67,560
Total accounts receivable	129,344	169,837
Less allowance for doubtful accounts	(5,272)	(4,868)	$ (4,280)	$ (4,774)
Accounts receivable	$ 124,072	$ 164,969