Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 43,145	$ 35,959
Adjustments to reconcile net income to cash flows provided by operating activities:
Depreciation and amortization	12,241	10,943
Stock-based compensation expense	3,902	3,140
Excess tax benefits from stock-based compensation	5,239	0
Other non-cash items	1,139	(166)
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net	(71,155)	(63,286)
Inventories, net	1,847	8,497
Prepaid expenses and other assets	(2,181)	(2,197)
Accounts payable, trade	18,146	18,692
Accrued expenses and other liabilities	10,433	32,116
Net cash flows provided by operating activities	22,756	43,698
Cash flows from investing activities:
Capital expenditures	(12,020)	(6,458)
Acquisitions of businesses, net of cash acquired	(10,689)	(18,100)
Proceeds from sales of fixed assets	119	234
Other investing activities	80	(151)
Net cash flows used for investing activities	(22,510)	(24,475)
Cash flows from financing activities:
Exercise of stock-based awards, net of shares tendered for payment of taxes	(7,650)	(3,196)
Proceeds from line of credit borrowings	0	81,458
Repayments under line of credit borrowings	0	(81,458)
Payment of dividends	12,442	0
Payment of contingent consideration related to acquisitions	(1,884)	(415)
Other financing activities	(59)	0
Net cash flows used for financing activities	(22,035)	(3,611)
Net (decrease) increase in cash and cash equivalents	(21,789)	15,612
Cash and cash equivalents at beginning of period	86,170	12,305
Cash and cash equivalents at end of period	64,381	27,917
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	483	521
Cash paid during the period for income taxes, net of refunds	2,072	122
Purchase of property and equipment in accrued expenses	$ 2,212	$ 459