Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 39,042	$ 32,595
Adjustments to reconcile net income to cash flows provided by operating activities:
Depreciation and amortization	20,388	19,211
Stock-based compensation expense	8,224	4,703
Other non-cash items	1,787	889
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net	(32,829)	(27,801)
Inventories	1,246	(5,753)
Prepaid expenses and other assets	4,090	(6,993)
Accounts payable	10,042	17,650
Accrued expenses and other liabilities	9,681	10,086
Net cash flows provided by operating activities	61,671	44,587
Cash flows from investing activities:
Capital expenditures	(26,080)	(22,010)
Acquisitions of businesses	(1,451)	(1,473)
Proceeds from sales of fixed assets	1,381	5,397
Other investing activities	(117)	(88)
Net cash flows used for investing activities	(26,267)	(18,174)
Cash flows from financing activities:
Proceeds from exercise of stock options	11,817	2,840
Proceeds from line of credit borrowings	135,452	37,702
Repayments under line of credit borrowings	(135,452)	(37,702)
Payment of contingent consideration related to acquisitions	(4,287)	(3,253)
Net cash flows provided by (used for) financing activities	7,530	(413)
Net increase in cash	42,934	26,000
Cash and cash equivalents at beginning of period	9,939	6,584
Cash and cash equivalents at end of period	52,873	32,584
Supplemental disclosure of cash flow information:
Interest	226	289
Income taxes, net of refunds	$ 19,276	$ 16,121