Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Net income	$ 113,876	$ 79,532
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets	(1,768)	(147)
Depreciation and amortization	29,049	26,881
Loss in equity method investment, before tax	52	53
Gain on bargain purchase of a business	0	(6,336)
Gain on disposal of a business	0	(443)
Deferred income taxes	2,061	2,552
Noncash compensation related to stock plans	8,773	11,816
Provision of doubtful accounts	361	79
Foreign exchange gain on capital repatriation	(1,604)	0
Changes in operating assets and liabilities, net of acquisitions:
Trade accounts receivable	(58,678)	(40,607)
Inventories	(29,233)	1,813
Trade accounts payable	14,254	698
Income taxes payable	9,801	1,686
Accrued profit sharing trust contributions	(486)	(902)
Accrued cash profit sharing and commissions	3,716	2,468
Other current assets	5,099	132
Accrued liabilities	13,464	5,291
Long-term liabilities	(373)	(234)
Accrued workers’ compensation	(139)	(21)
Other noncurrent assets	(256)	280
Net cash provided by operating activities	107,969	84,591
Cash flows from investing activities
Capital expenditures	(24,714)	(45,106)
Asset acquisitions, net of cash acquired	0	(27,921)
Proceeds from sale of property and equipment	3,539	617
Proceeds from sale of a business	0	9,613
Net cash used in investing activities	(21,175)	(62,797)
Cash flows from financing activities
Deferred and contingent consideration paid for asset acquisitions	0	(205)
Repurchase of common stock	(49,490)	(20,000)
Repayment of long-term borrowings and capital leases	(702)	(360)
Repayment of debt and line of credit borrowings	0	(133)
Issuance of common stock	695	3,566
Dividends paid	(29,738)	(27,044)
Cash paid on behalf of employees for shares withheld	(5,128)	(5,166)
Net cash used in financing activities	(84,363)	(49,342)
Effect of exchange rate changes on cash and cash equivalents	(3,984)	5,182
Net decrease in cash and cash equivalents	(1,553)	(22,366)
Cash and cash equivalents at beginning of period	168,514	226,537
Cash and cash equivalents at end of period	166,961	204,171
Noncash activity during the period
Noncash capital expenditures	212	892
Dividends declared but not paid	10,134	19,891
Contingent consideration for acquisition	0	1,314
Issuance of Company’s common stock for compensation	$ 465	$ 412