Recent Accounting Standards (Details) - USD ($) $ 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	Dec. 31, 2016
Assets
Accounts receivable, less allowances	$ 378,790		$ 378,790		$ 362,479	$ 348,943
Inventories	251,047		251,047		233,054	241,962
Prepaid expenses and other current assets	55,943		55,943		47,105	32,526
Deferred income taxes	14,857		14,857		11,171	12,161
Liabilities
Accrued liabilities	202,209		202,209		194,777	181,241
Deferred income taxes	70,296		70,296		73,891	73,505
Stockholders' equity
Retained earnings	1,302,640		1,302,640		1,211,018	1,206,723
Accumulated other non-owner changes to equity	(157,137)	$ (139,181)	(157,137)	$ (139,181)		(106,399)	$ (200,828)
Consolidated Statement of Income
Net sales	375,315	364,493	741,975	706,295
Cost of sales	237,608	242,538	474,742	462,087
Operating profit	63,879	50,759	120,512	107,037
Income before income taxes	58,799	53,205	109,777	105,581
Income taxes	9,370	8,178	21,530	22,251
Net income	49,429	45,027	88,247	83,330
Other expense (income), net	947	(5,987)	2,710	(5,434)
Pensions [Member]
Consolidated Statement of Income
Curtailment gain	0	(7,217)	0	(7,217)
Settlement gain	0	(230)	0	(491)
Accounting Standards Update 2017-07 [Member]
Consolidated Statement of Income
Other expense (income), net		$ (6,378)		$ (5,848)
Accounting Standards Update 2018-02 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Stockholders' equity
Retained earnings	19,331		19,331
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Assets
Accounts receivable, less allowances	357,243		357,243			348,943
Inventories	259,177		259,177			241,962
Prepaid expenses and other current assets	41,624		41,624
Deferred income taxes	16,063		16,063			12,161
Liabilities
Accrued liabilities	180,531		180,531			181,241
Deferred income taxes	70,045		70,045			73,505
Stockholders' equity
Retained earnings	1,298,044		1,298,044			$ 1,206,723
Accumulated other non-owner changes to equity	(157,148)		(157,148)
Consolidated Statement of Income
Net sales	375,662		742,294
Cost of sales	237,651		475,468
Operating profit	64,183		120,105
Income before income taxes	59,103		109,370
Income taxes	9,445		21,427
Net income	49,658		87,943
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Assets
Accounts receivable, less allowances	21,547		21,547		13,536
Inventories	(8,130)		(8,130)		(8,908)
Prepaid expenses and other current assets	14,319		14,319		14,579
Deferred income taxes	(1,206)		(1,206)		(990)
Liabilities
Accrued liabilities	21,678		21,678		13,536
Deferred income taxes	251		251		386
Stockholders' equity
Retained earnings	4,596		4,596		$ 4,295
Accumulated other non-owner changes to equity	11		11
Consolidated Statement of Income
Net sales	(347)		(319)
Cost of sales	(43)		(726)
Operating profit	(304)		407
Income before income taxes	(304)		407
Income taxes	(75)		103
Net income	$ (229)		$ 304