Recently Adopted and Recently Issued Accounting Standards (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 19,577	$ 10,137
Adjustments to reconcile net income to net cash used by operating activities:
Deferred income tax expense (benefit)	4,635	(221)
Changes in assets and liabilities:
Accounts receivable	(4,848)	(27,882)
Inventories	(11,490)	(755)
Contract assets	(5,698)	0
Advances on contracts	(7,348)	(4,998)
Other assets and liabilities	(7,375)	1,205
Net Cash Provided by (Used in) Operating Activities	(8,243)	$ (6,124)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	(102)
Adjustments to reconcile net income to net cash used by operating activities:
Deferred income tax expense (benefit)	8
Changes in assets and liabilities:
Accounts receivable	136
Inventories	(11,402)
Contract assets	5,698
Advances on contracts	3,028
Other assets and liabilities	2,634
Net Cash Provided by (Used in) Operating Activities	0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	19,475
Adjustments to reconcile net income to net cash used by operating activities:
Deferred income tax expense (benefit)	4,643
Changes in assets and liabilities:
Accounts receivable	(4,712)
Inventories	(22,892)
Contract assets	0
Advances on contracts	(4,320)
Other assets and liabilities	(4,741)
Net Cash Provided by (Used in) Operating Activities	$ (8,243)