Revenue from Contracts with Customers - Impact of Adoption of New Accounting Principle (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Condensed Consolidated Statements of Financial Position:
Inventory	$ 125,885		$ 125,885			$ 112,557
Retained earnings	751,951		751,951			684,540
Condensed Consolidated Statement of Income
Net sales	226,863	$ 206,783	656,149	$ 612,035
Cost of sales	147,733	124,595	423,741	368,951
Income tax expense	8,870	15,396	22,014	38,979
Net income	$ 19,734	$ 25,532	$ 63,199	$ 73,460
Basic earnings per share (in dollars per share)	$ 1.07	$ 1.40	$ 3.44	$ 4.05
Diluted earnings per share (in dollars per share)	$ 1.06	$ 1.37	$ 3.39	$ 3.97
Condensed Consolidated Statement of Cash Flows:
Deferred income taxes			$ (17)	$ 10,452
Contract assets			(20,260)	0
Inventories			(11,840)	(16,573)
Other, net			3,216	956
Net cash provided by operating activities			33,424	$ 99,851
Accounting Standards Update 2014-09
Condensed Consolidated Statements of Financial Position:
Contract assets	$ 20,260		20,260		$ 18,099
Inventory	125,885		125,885		100,250
Deferred income tax liability	10,936		10,936		12,286
Retained earnings	751,951		751,951		688,752
Under ASC 605
Condensed Consolidated Statement of Income
Net sales	228,536		653,988
Cost of sales	148,870		422,272
Income tax expense	9,020		21,831
Net income	$ 20,120		$ 62,690
Basic earnings per share (in dollars per share)	$ 1.09		$ 3.41
Diluted earnings per share (in dollars per share)	$ 1.08		$ 3.36
Condensed Consolidated Statement of Cash Flows:
Deferred income taxes			$ (200)
Contract assets			0
Inventories			(25,617)
Other, net			(2,575)
Net cash provided by operating activities			33,424
Under ASC 605 | Accounting Standards Update 2014-09
Condensed Consolidated Statements of Financial Position:
Contract assets	$ 0		0			0
Inventory	139,662		139,662			112,557
Deferred income tax liability	9,172		9,172			10,706
Retained earnings	747,232		747,232			$ 684,540
Impact of Adoption
Condensed Consolidated Statement of Income
Net sales	(1,673)		2,161
Cost of sales	(1,137)		1,469
Income tax expense	(150)		183
Net income	$ (386)		$ 509
Basic earnings per share (in dollars per share)	$ (0.02)		$ 0.03
Diluted earnings per share (in dollars per share)	$ (0.02)		$ 0.03
Condensed Consolidated Statement of Cash Flows:
Deferred income taxes			$ 183
Contract assets			(20,260)
Inventories			13,777
Other, net			5,791
Net cash provided by operating activities			0
Impact of Adoption | Accounting Standards Update 2014-09
Condensed Consolidated Statements of Financial Position:
Contract assets	$ 20,260		20,260		18,099
Inventory	(13,777)		(13,777)		(12,307)
Deferred income tax liability	1,764		1,764		1,580
Retained earnings	$ 4,719		$ 4,719		$ 4,212