Condensed Consolidated Statements Of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 34,366,000	$ 47,336,000
Adjustments to reconcile net income to cash flows provided by operating activities:
Depreciation and amortization	18,449,000	15,275,000
Stock-based compensation expense	3,733,000	5,543,000
Other non-cash items	611,000	(1,127,000)
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net	(57,753,000)	(71,073,000)
Inventories, net	16,052,000	(17,232,000)
Prepaid expenses and other assets	10,268,000	(3,185,000)
Accounts payable, trade	11,581,000	8,114,000
Accrued expenses and other liabilities	15,278,000	11,246,000
Net cash flows provided by operating activities	52,585,000	(5,103,000)
Cash flows from investing activities:
Capital expenditures	(24,442,000)	(26,004,000)
Acquisitions of businesses, net of cash acquired	0	(138,570,000)
Proceeds from note receivable	0	155,000
Other investing activities	61,000	(35,000)
Net cash flows used in investing activities	(24,381,000)	(164,454,000)
Cash flows from financing activities:
Exercise of stock-based awards, net of shares tendered for payment of taxes	(6,348,000)	(14,085,000)
Proceeds from line of credit borrowings	175,660,000	474,000,000
Repayments under line of credit borrowings	(182,720,000)	(297,000,000)
Payment of dividends	14,999,000	13,858,000
Other financing activities	(157,000)	(556,000)
Net cash flows provided by (used in) financing activities	(28,564,000)	148,501,000
Effect of exchange rate changes on cash and cash equivalents	(251,000)	0
Net decrease in cash and cash equivalents	(611,000)	(21,056,000)
Cash and cash equivalents at beginning of period	14,928,000	26,049,000
Cash and cash equivalents at end of period	14,317,000	4,993,000
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	2,394,000	1,012,000
Cash paid during the period for income taxes, net of refunds	59,000	(11,000)
Purchase of property and equipment in accrued expenses	$ 1,202,000	$ 3,711,000