Revenue from Contracts with Customers (Impact of Adoption of Accounting Principles) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Consolidated Statements of Financial Position:
Contract assets	$ 22,728				$ 0				$ 22,728	$ 0
Inventories	132,637				112,557				132,637	112,557
Deferred income taxes	10,806								10,806
Retained earnings	776,403				684,540				776,403	684,540
Consolidated Statements of Operations:
Net sales	222,942	$ 226,863	$ 214,675	$ 214,611	209,008	$ 206,783	$ 201,424	$ 203,828	879,091	821,043	$ 656,314
Cost of sales									568,308	502,468	406,829
Income tax expense									22,938	52,466	33,997
Net income									$ 87,651	$ 80,459	$ 48,283
Basic earnings per share (in dollars per share)									$ 4.77	$ 4.43	$ 2.68
Diluted earnings per share (in dollars per share)									$ 4.70	$ 4.34	$ 2.65
Consolidated Statements of Cash Flows:
Deferred income taxes									$ (3,325)	$ 17,513	$ 7,382
Contract assets									(22,728)	0	0
Inventories									(19,013)	(14,208)	9,689
Other, net									991	5,885	(4,715)
Net cash provided by operating activities									66,820	138,982	$ 116,967
Accounting Standards Update 2014-09
Consolidated Statements of Financial Position:
Contract assets												$ 18,099
Inventories												100,250
Deferred income taxes												12,286
Retained earnings												688,752
Calculated under Revenue Guidance in Effect before Topic 606
Consolidated Statements of Financial Position:
Contract assets	0								0
Inventories	148,092								148,092
Deferred income taxes	8,846								8,846
Retained earnings	771,090								771,090
Consolidated Statements of Operations:
Net sales									874,462
Cost of sales									565,160
Income tax expense									22,558
Net income									$ 86,550
Basic earnings per share (in dollars per share)									$ 4.71
Diluted earnings per share (in dollars per share)									$ 4.64
Consolidated Statements of Cash Flows:
Deferred income taxes									$ (3,705)
Contract assets									0
Inventories									(34,468)
Other, net									(4,801)
Net cash provided by operating activities									66,820
Calculated under Revenue Guidance in Effect before Topic 606 | Accounting Standards Update 2014-09
Consolidated Statements of Financial Position:
Contract assets					0					0
Inventories					112,557					112,557
Deferred income taxes					10,706					10,706
Retained earnings					$ 684,540					$ 684,540
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Consolidated Statements of Financial Position:
Contract assets	22,728								22,728			18,099
Inventories	(15,455)								(15,455)			(12,307)
Deferred income taxes	1,960								1,960			1,580
Retained earnings	$ 5,313								5,313			$ 4,212
Consolidated Statements of Operations:
Net sales									4,629
Cost of sales									3,148
Income tax expense									380
Net income									$ 1,101
Basic earnings per share (in dollars per share)									$ 0.06
Diluted earnings per share (in dollars per share)									$ 0.06
Consolidated Statements of Cash Flows:
Deferred income taxes									$ 380
Contract assets									(22,728)
Inventories									15,455
Other, net									5,792
Net cash provided by operating activities									$ 0