Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Statement of Cash Flows [Abstract]
Net income	$ 72,341	$ 53,156
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets	(763)	(57)
Depreciation and amortization	21,485	21,664
Write-off of software development project	153	3,140
Gain on contingent consideration adjustment	0	(245)
Deferred income taxes	1,481	1,701
Noncash compensation related to stock plans	9,707	9,528
Excess tax benefit of options exercised and restricted stock units vested	(162)	(67)
Provision (recovery) for doubtful accounts	(131)	153
Changes in operating assets and liabilities, net of acquisitions:
Trade accounts receivable	(35,463)	(42,851)
Inventories	(22,992)	13,567
Trade accounts payable	2,806	3,026
Income taxes payable	6,745	8,151
Accrued profit sharing trust contributions	(637)	(997)
Accrued cash profit sharing and commissions	8,636	6,577
Other current assets	(2,751)	4,293
Accrued liabilities	2,615	(6,716)
Long-term liabilities	(1,222)	(3,093)
Accrued workers’ compensation	(432)	385
Other noncurrent assets	1,471	954
Net cash provided by operating activities	62,887	72,269
Cash flows from investing activities
Capital expenditures	(29,934)	(19,163)
Asset acquisitions, net of cash acquired	(5,361)	(779)
Proceeds from sale of property and equipment	1,278	136
Loan repayment by customer	0	244
Net cash used in investing activities	(34,017)	(19,562)
Cash flows from financing activities
Deferred and contingent consideration paid for asset acquisition	(27)	(1,177)
Repurchase of common stock	(53,502)	(47,144)
Repayment of debt and line of credit borrowings	0	(18)
Debt issuance costs	(1,125)	0
Issuance of common stock	6,695	7,019
Excess tax benefit of options exercised and restricted stock units vested	162	67
Dividends paid	(24,152)	(21,628)
Net cash used in financing activities	(71,949)	(62,881)
Effect of exchange rate changes on cash and cash equivalents	2,974	(7,338)
Net decrease in cash and cash equivalents	(40,105)	(17,512)
Cash and cash equivalents at beginning of period	258,825	260,307
Cash and cash equivalents at end of period	218,720	242,795
Noncash activity during the period
Noncash capital expenditures	(726)	0
Dividends declared but not paid	8,559	7,872
Issuance of Company’s common stock for compensation	$ 315	$ 552