Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 47,336	$ 43,145
Adjustments to reconcile net income to cash flows provided by (used in) operating activities:
Depreciation and amortization	15,275	12,241
Stock-based compensation expense	5,543	3,902
Other non-cash items	(1,127)	1,139
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net	(71,073)	(71,155)
Inventories, net	(17,232)	1,847
Prepaid expenses and other assets	(3,185)	(2,181)
Accounts payable, trade	8,114	18,146
Accrued expenses and other liabilities	11,246	14,627
Net cash flows provided by (used in) operating activities	(5,103)	21,711
Cash flows from investing activities:
Capital expenditures	(26,004)	(12,020)
Acquisitions of businesses, net of cash acquired	(138,570)	(10,689)
Proceeds from sales of fixed assets	155	119
Other investing activities	(35)	80
Net cash flows used in investing activities	(164,454)	(22,510)
Cash flows from financing activities:
Exercise of stock-based awards, net of shares tendered for payment of taxes	(14,085)	(7,650)
Proceeds from line of credit borrowings	474,000	0
Repayments under line of credit borrowings	(297,000)	0
Payment of dividends	13,858	12,442
Payment of contingent consideration related to acquisitions	0	(839)
Other financing activities	(556)	(59)
Net cash flows provided by (used in) financing activities	148,501	(20,990)
Net decrease in cash and cash equivalents	(21,056)	(21,789)
Cash and cash equivalents at beginning of period	26,049	86,170
Cash and cash equivalents at end of period	4,993	64,381
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	1,012	483
Cash paid during the period for income taxes, net of refunds	(11)	2,072
Purchase of property and equipment in accrued expenses	$ 3,711	$ 2,212