Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Net income	$ 62,239	$ 69,515
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets and other	(262)	(1,287)
Depreciation and amortization	19,515	19,633
Noncash lease expense	3,243
Deferred income taxes and other long-term liabilities	1,911	1,546
Noncash compensation related to stock plans	6,600	6,020
Provision of doubtful accounts	98	290
Changes in operating assets and liabilities, net of acquisitions:
Trade accounts receivable	(45,078)	(76,838)
Inventories	9,708	(7,739)
Trade accounts payable	4,318	19,193
Other current assets	(1,269)	3,794
Accrued liabilities and other current liabilities	(3,852)	20,254
Other noncurrent assets and liabilities	(3,590)	983
Net cash provided by operating activities	53,581	55,364
Cash flows from investing activities
Capital expenditures	(15,259)	(19,040)
Asset acquisitions, net of cash acquired	(3,492)	0
Proceeds from sale of property and equipment	2,493	2,017
Net cash used in investing activities	(16,258)	(17,023)
Cash flows from financing activities
Repurchase of common stock	(30,000)	(25,439)
Proceeds from line of credit	10,742	0
Repayments of line of credit and capital leases	(10,726)	(437)
Issuance of common stock for exercise of options	0	695
Dividends paid	(19,726)	(19,546)
Cash paid on behalf of employees for shares withheld	(5,899)	(5,111)
Net cash used in financing activities	(55,609)	(49,838)
Effect of exchange rate changes on cash and cash equivalents	(163)	(1,982)
Net decrease in cash and cash equivalents	(18,449)	(13,479)
Cash and cash equivalents at beginning of period	160,180	168,514
Cash and cash equivalents at end of period	141,731	155,035
Noncash activity during the period
Noncash capital expenditures	1,636	290
Dividends declared but not paid	10,284	10,190
Issuance of Company’s common stock for compensation	$ 292	$ 465