Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Statement of Cash Flows [Abstract]
Net income	$ 42,544	$ 31,560
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets	(682)	(31)
Depreciation and amortization	14,878	14,716
Write-off of software development project	153	0
Gain on contingent consideration adjustment	0	(245)
Deferred income taxes	1,512	2,286
Noncash compensation related to stock plans	6,323	6,588
Excess tax benefit of options exercised and restricted stock units vested	(41)	(60)
Provision (recovery) for doubtful accounts	(171)	17
Changes in operating assets and liabilities, net of acquisitions:
Trade accounts receivable	(39,030)	(50,480)
Inventories	(22,043)	2,092
Trade accounts payable	6,203	4,651
Income taxes payable	8,187	9,363
Accrued profit sharing trust contributions	(2,102)	(2,211)
Accrued cash profit sharing and commissions	7,105	7,705
Other current assets	(849)	1,009
Accrued liabilities	(4,121)	(3,499)
Long-term liabilities	(3,423)	(269)
Accrued workers’ compensation	(439)	356
Other noncurrent assets	3,739	1,204
Net cash provided by operating activities	17,743	24,752
Cash flows from investing activities
Capital expenditures	(17,549)	(13,534)
Asset acquisitions, net of cash acquired	0	(779)
Proceeds from sale of property and equipment	1,198	113
Loan repayment by customer	0	243
Net cash used in investing activities	(16,351)	(13,957)
Cash flows from financing activities
Deferred and contingent consideration paid for asset acquisition	(27)	(1,177)
Repurchase of common stock	(3,502)	(8,464)
Repayment of debt and line of credit borrowings	0	(17)
Issuance of common stock	2,525	5,576
Excess tax benefit of options exercised and restricted stock units vested	41	60
Dividends paid	(15,442)	(13,768)
Net cash used in financing activities	(16,405)	(17,790)
Effect of exchange rate changes on cash and cash equivalents	2,525	(4,700)
Net decrease in cash and cash equivalents	(12,488)	(11,695)
Cash and cash equivalents at beginning of period	258,825	260,307
Cash and cash equivalents at end of period	246,337	248,612
Noncash activity during the period
Dividends declared but not paid	8,712	7,896
Issuance of Company’s common stock for compensation	$ 315	$ 552