Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Statement of Cash Flows [Abstract]
Net income	$ 51,335	$ 42,544
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets	0	(682)
Depreciation and amortization	16,395	14,878
Write-off of software development project	0	153
Loss in equity method investment, before tax	41	0
Gain on bargain purchase of a business	(8,388)	0
Deferred income taxes	1,183	1,512
Noncash compensation related to stock plans	11,185	6,323
Excess tax benefit of options exercised and restricted stock units vested	0	(41)
Recovery of doubtful accounts	(25)	(171)
Changes in operating assets and liabilities, net of acquisitions:
Trade accounts receivable	(52,132)	(39,030)
Inventories	(16,403)	(22,043)
Trade accounts payable	2,816	6,203
Income taxes payable	(2,454)	8,187
Accrued profit sharing trust contributions	(2,408)	(2,102)
Accrued cash profit sharing and commissions	3,635	7,105
Other current assets	(255)	(849)
Accrued liabilities	2,739	(148)
Long-term liabilities	875	(3,423)
Accrued workers’ compensation	221	(439)
Other noncurrent assets	(633)	3,739
Net cash provided by operating activities	7,727	21,716
Cash flows from investing activities
Capital expenditures	(32,288)	(17,549)
Asset acquisitions, net of cash acquired	(26,289)	0
Proceeds from sale of property and equipment	86	1,198
Net cash used in investing activities	(58,491)	(16,351)
Cash flows from financing activities
Deferred and contingent consideration paid for asset acquisition	(205)	(27)
Repurchase of common stock	(20,000)	(3,502)
Capital lease borrowings	2,135	0
Repayment of debt and line of credit borrowings	(133)	0
Issuance of common stock	1,297	2,525
Excess tax benefit of options exercised and restricted stock units vested	0	41
Dividends paid	(17,116)	(15,442)
Cash paid on behalf of employees for shares withheld	(5,155)	(3,973)
Net cash used in financing activities	(39,177)	(20,378)
Effect of exchange rate changes on cash and cash equivalents	4,354	2,525
Net decrease in cash and cash equivalents	(85,587)	(12,488)
Cash and cash equivalents at beginning of period	226,537	258,825
Cash and cash equivalents at end of period	140,950	246,337
Noncash activity during the period
Noncash capital expenditures	3,938	1,017
Dividends declared but not paid	9,927	8,712
Contingent consideration for acquisition	1,000	0
Issuance of Company’s common stock for compensation	$ 412	$ 315