Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Statement of Cash Flows [Abstract]
Net income	$ 90,305	$ 62,239
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of assets and other	(147)	(262)
Depreciation and amortization	19,739	19,515
Noncash lease expense	4,025	3,243
Deferred income taxes	1,973	1,911
Noncash compensation related to stock plans	5,428	6,600
Provision (benefit) of doubtful accounts	(35)	98
Changes in operating assets and liabilities:
Trade accounts receivable	(95,875)	(45,078)
Inventories	(14,377)	9,708
Trade accounts payable	15,268	4,318
Other current assets	(4,529)	(1,269)
Accrued liabilities and other current liabilities	22,923	(3,852)
Other noncurrent assets and liabilities	(1,932)	(3,590)
Net cash provided by operating activities	42,766	53,581
Cash flows from investing activities
Capital expenditures	(14,083)	(15,259)
Asset acquisitions, net of cash acquired	0	(3,492)
Proceeds from sale of property and equipment	639	2,493
Net cash used in investing activities	(13,444)	(16,258)
Cash flows from financing activities
Repurchase of common stock	(62,679)	(30,000)
Proceeds from line of credit	159,412	10,742
Repayments of line of credit and capital leases	(10,387)	(10,726)
Payments of Debt Issuance Costs	(712)	0
Dividends paid	(20,158)	(19,726)
Cash paid on behalf of employees for shares withheld	(7,743)	(5,899)
Net cash provided by (used) in financing activities	57,733	(55,609)
Effect of exchange rate changes on cash and cash equivalents	(1,817)	(163)
Net increase (decrease) in cash and cash equivalents	85,238	(18,449)
Cash and cash equivalents at beginning of period	230,210	160,180
Cash and cash equivalents at end of period	315,448	141,731
Noncash activity during the period
Noncash capital expenditures	1,308	1,636
Dividends declared but not paid	9,989	10,284
Issuance of Company’s common stock for compensation	$ 322	$ 292