Revenue from Contracts with Customers - Impact of Adoption of New Accounting Principle (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Condensed Consolidated Statements of Financial Position:
Inventory	$ 117,739		$ 117,739			$ 112,557
Retained earnings	732,217		732,217			684,540
Condensed Consolidated Statement of Income
Net sales	214,675	$ 201,424	429,286	$ 405,252
Cost of sales	138,003	120,878	276,007	244,356
Income tax expense	8,373	10,697	13,144	23,583
Net income	$ 17,329	$ 20,896	$ 43,465	$ 47,928
Basic earnings per share (in dollars per share)	$ 0.94	$ 1.15	$ 2.37	$ 2.65
Diluted earnings per share (in dollars per share)	$ 0.93	$ 1.13	$ 2.33	$ 2.60
Condensed Consolidated Statement of Cash Flows:
Deferred income taxes			$ 3,879	$ 4,813
Contract assets			(21,933)	0
Inventories			(6,489)	(6,464)
Other, net			3,287	1,703
Net cash provided by operating activities			22,818	$ 64,489
Accounting Standards Update 2014-09
Condensed Consolidated Statements of Financial Position:
Contract assets	$ 21,933		21,933		$ 18,099
Inventory	117,739		117,739		100,250
Deferred income taxes	3,501		3,501		12,286
Retained earnings	732,217		732,217		688,752
Under ASC 605
Condensed Consolidated Statement of Income
Net sales	214,782		425,452
Cost of sales	138,076		273,400
Income tax expense	8,373		12,811
Net income	$ 17,363		$ 42,571
Basic earnings per share (in dollars per share)	$ 0.94		$ 2.32
Diluted earnings per share (in dollars per share)	$ 0.93		$ 2.28
Condensed Consolidated Statement of Cash Flows:
Deferred income taxes			$ 3,546
Contract assets			0
Inventories			(21,403)
Other, net			(2,505)
Net cash provided by operating activities			22,818
Under ASC 605 | Accounting Standards Update 2014-09
Condensed Consolidated Statements of Financial Position:
Contract assets	$ 0		0			0
Inventory	132,653		132,653			112,557
Deferred income taxes	1,588		1,588			10,706
Retained earnings	727,111		727,111			$ 684,540
Impact of Adoption
Condensed Consolidated Statement of Income
Net sales	(107)		3,834
Cost of sales	(73)		2,607
Income tax expense	0		333
Net income	$ (34)		$ 894
Basic earnings per share (in dollars per share)	$ 0.00		$ 0.05
Diluted earnings per share (in dollars per share)	$ 0.00		$ 0.05
Condensed Consolidated Statement of Cash Flows:
Deferred income taxes			$ 333
Contract assets			(21,933)
Inventories			14,914
Other, net			5,792
Net cash provided by operating activities			0
Impact of Adoption | Accounting Standards Update 2014-09
Condensed Consolidated Statements of Financial Position:
Contract assets	$ 21,933		21,933		18,099
Inventory	(14,914)		(14,914)		(12,307)
Deferred income taxes	1,913		1,913		1,580
Retained earnings	$ 5,106		$ 5,106		$ 4,212