Recent Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Accounts receivable, less allowances	$ 394,910		$ 362,479	$ 348,943
Inventories	250,217		233,054	241,962
Prepaid expenses and other current assets	54,544		47,105
Deferred income taxes	9,848		11,171	12,161
Liabilities
Accrued liabilities	204,820		194,777	181,241
Deferred income taxes	75,192		73,891	73,505
Stockholders' equity
Retained earnings	1,261,540		1,211,018	1,206,723
Accumulated other non-owner changes to equity	(95,217)	$ (180,871)		(106,399)	$ (200,828)
Consolidated Statement of Income
Net sales	366,660	341,802
Cost of sales	237,134	219,549
Operating profit	56,633	56,278
Income before income taxes	50,978	52,376
Income taxes	12,160	14,073
Net income	38,818	38,303
Other expense (income), net	1,763	$ 553
Accounting Standards Update 2017-07 [Member]
Consolidated Statement of Income
Other expense (income), net	530
Accounting Standards Update 2018-02 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
Stockholders' equity
Retained earnings	19,331
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Assets
Accounts receivable, less allowances	370,327			348,943
Inventories	258,440			241,962
Prepaid expenses and other current assets	39,745			32,526
Deferred income taxes	11,050			12,161
Liabilities
Accrued liabilities	180,084			181,241
Deferred income taxes	74,855			73,505
Stockholders' equity
Retained earnings	1,256,712			$ 1,206,723
Accumulated other non-owner changes to equity	(95,273)
Consolidated Statement of Income
Net sales	366,632
Cost of sales	237,817
Operating profit	55,922
Income before income taxes	50,267
Income taxes	11,982
Net income	38,285
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Assets
Accounts receivable, less allowances	24,583		13,536
Inventories	(8,223)		(8,908)
Prepaid expenses and other current assets	14,799		14,579
Deferred income taxes	(1,202)		(990)
Liabilities
Accrued liabilities	24,736		13,536
Deferred income taxes	337		386
Stockholders' equity
Retained earnings	4,828		$ 4,295
Accumulated other non-owner changes to equity	56
Consolidated Statement of Income
Net sales	28
Cost of sales	(683)
Operating profit	711
Income before income taxes	711
Income taxes	178
Net income	$ 533