Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Cash Flows [Abstract]
Net income	$ 25,429	$ 23,121
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets	(1,184)	(51)
Depreciation and amortization	9,688	8,363
Loss in equity method investment, before tax	24	28
Gain on bargain purchase of a business	0	(8,388)
Deferred income taxes	1,448	1,163
Noncash compensation related to stock plans	3,116	7,976
Provision of doubtful accounts	222	13
Changes in operating assets and liabilities, net of acquisitions:
Trade accounts receivable	(30,764)	(30,254)
Inventories	(3,071)	(9,796)
Trade accounts payable	11,451	3,209
Income taxes payable	721	3,681
Accrued profit sharing trust contributions	(4,326)	(4,036)
Accrued cash profit sharing and commissions	(346)	(1,287)
Other current assets	1,923	(695)
Accrued liabilities	(983)	(845)
Long-term liabilities	3,763	87
Accrued workers’ compensation	12	9
Other noncurrent assets	(5)	210
Net cash provided by (used in) operating activities	17,118	(7,492)
Cash flows from investing activities
Capital expenditures	(10,935)	(13,629)
Asset acquisitions, net of cash acquired	0	(26,289)
Proceeds from sale of property and equipment	1,239	53
Net cash used in investing activities	(9,696)	(39,865)
Cash flows from financing activities
Deferred and contingent consideration paid for asset acquisitions	0	(65)
Repurchase of common stock	(24,999)	0
Repayment of long-term borrowings and capital leases	(174)	0
Issuance of common stock	695	314
Dividends paid	(9,818)	(8,538)
Cash paid on behalf of employees for shares withheld	(5,027)	(5,124)
Net cash used in financing activities	(39,323)	(13,413)
Effect of exchange rate changes on cash and cash equivalents	800	1,292
Net decrease in cash and cash equivalents	(31,101)	(59,478)
Cash and cash equivalents at beginning of period	168,514	226,537
Cash and cash equivalents at end of period	137,413	167,059
Noncash activity during the period
Noncash capital expenditures	1,567	4,817
Capital lease obligations	0	2,131
Dividends declared but not paid	10,190	8,578
Contingent consideration for acquisition	0	1,139
Issuance of Company’s common stock for compensation	$ 465	$ 412