Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Statement of Cash Flows [Abstract]
Net income	$ 126,633	$ 92,617	$ 89,734
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets	(10,579)	(160)	(780)
Depreciation and amortization	39,393	33,724	27,927
Write-off of software development project	0	676	2,212
Loss in equity method investment, before tax	63	86	0
Gain (adjustment) on bargain purchase of a business	0	(6,336)	0
Loss on disposal of a business	0	211	0
Impairment of goodwill	6,686	0	0
Deferred income taxes	4,950	6,299	(869)
Noncash compensation related to stock plans	11,176	13,908	13,946
Excess tax benefit of options exercised and restricted stock units vested	0	0	(273)
Recovery (provision) of doubtful accounts	569	66	(83)
Foreign Currency Transaction Gain, before Tax	1,841	0	0
Changes in operating assets and liabilities, net of effects of acquisitions and dispositions:
Trade accounts receivable	(12,573)	(17,822)	(7,548)
Inventories	(26,425)	(6,580)	(36,617)
Other current assets	5,297	(2,016)	(2,180)
Other noncurrent assets	533	513	336
Trade accounts payable	4,670	1,157	5,785
Accrued liabilities	9,136	10,130	4,290
Accrued profit sharing trust contributions	755	498	757
Accrued cash profit sharing and commissions	1,491	(1,246)	2,064
Long-term liabilities	(2,276)	(718)	242
Accrued workers’ compensation	(173)	(343)	(1,024)
Income taxes payable	2,595	(5,599)	1,046
Net cash provided by operating activities	160,080	119,065	98,965
Cash flows from investing activities
Capital expenditures	(29,310)	(58,041)	(42,002)
Assets acquisitions, net of cash acquired	(2,007)	(27,921)	(5,361)
Equity investments	0	0	(2,500)
Proceeds from sale of property and equipment	21,068	681	1,320
Proceeds from sale of a business	0	9,466	0
Net cash used in investing activities	(10,249)	(75,815)	(48,543)
Cash flows from financing activities
Repayment of long-term borrowings and capital leases	(968)	(354)	0
Repayment of debt and line of credit borrowings	821	(400)	0
Deferred and contingent consideration paid for asset acquisitions	(364)	(205)	(27)
Debt issuance costs	0	0	(1,125)
Repurchase of common stock	(110,540)	(70,000)	(53,502)
Issuance of Company’s common stock	695	6,610	7,976
Excess tax benefit of options exercised and restricted stock units vested	0	0	273
Dividends paid	(39,891)	(36,981)	(32,711)
Cash paid on behalf of employees for shares withheld	(5,146)	(5,341)	(4,018)
Net cash used in financing activities	(155,393)	(106,671)	(83,134)
Effect of exchange rate changes on cash	(2,772)	5,398	424
Net decrease in cash and cash equivalents	(8,334)	(58,023)	(32,288)
Cash and cash equivalents at beginning of year	168,514	226,537	258,825
Cash and cash equivalents at end of year	160,180	168,514	226,537
Cash paid during the year for
Interest	160	121	284
Income taxes	40,123	50,832	49,425
Noncash activity during the year for
Noncash capital expenditures	908	1,533	2,318
Capital lease obligations	0	3,750	0
Contingent consideration for acquisition	0	1,314	0
Issuance of Company's common stock for compensation	465	411	315
Dividends declared but not paid	$ 9,988	$ 9,954	$ 8,535