Recently Adopted and Recently Issued Accounting Standards (Details 3) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	$ 42,711	$ 19,731	$ 62,288	$ 29,868
Adjustments to reconcile net income to net cash used by operating activities:
Deferred income tax expense			340	3,433
Changes in assets and liabilities:
Accounts receivable			(21,445)	(42,806)
Inventories			(11,175)	(6,296)
Contract assets			(1,393)	0
Advances on contracts			(13,116)	(1,479)
Other assets and liabilities			(11,334)	4,990
Net Cash Provided by (Used in) Operating Activities			46,699	$ 46,779
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	1,190		1,088
Adjustments to reconcile net income to net cash used by operating activities:
Deferred income tax expense			(4)
Changes in assets and liabilities:
Accounts receivable			(797)
Inventories			(22,661)
Contract assets			1,393
Advances on contracts			15,966
Other assets and liabilities			5,015
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	$ 43,901		63,376
Adjustments to reconcile net income to net cash used by operating activities:
Deferred income tax expense			336
Changes in assets and liabilities:
Accounts receivable			(22,242)
Inventories			(33,836)
Contract assets			0
Advances on contracts			2,850
Other assets and liabilities			(6,319)
Net Cash Provided by (Used in) Operating Activities			$ 46,699