Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 24,237	$ 22,824
Adjustments to reconcile net income to cash flows provided by operating activities:
Depreciation and amortization	13,453	12,361
Stock-based compensation expense	5,844	3,069
Other non-cash items	1,624	1,131
Changes in assets and liabilities, net of acquisitions of businesses:
Accounts receivable, net	(37,520)	(28,280)
Inventories	(2,367)	1,227
Prepaid expenses and other assets	3,573	(4,642)
Accounts payable	11,696	28,630
Accrued expenses and other liabilities	12,499	12,241
Net cash flows provided by operating activities	33,039	48,561
Cash flows from investing activities:
Capital expenditures	(17,545)	(13,154)
Acquisitions of businesses	(1,451)	(1,473)
Proceeds from sales of fixed assets	70	2,123
Other investing activities	(48)	(48)
Net cash flows used for investing activities	(18,974)	(12,552)
Cash flows from financing activities:
Proceeds from exercise of stock options	10,686	1,471
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	(2,813)	(1,550)
Net cash flows provided by (used for) financing activities	7,873	(79)
Net increase in cash	21,938	35,930
Cash and cash equivalents at beginning of period	9,939	6,584
Cash and cash equivalents at end of period	31,877	42,514
Supplemental disclosure of cash flow information:
Interest	159	216
Income taxes, net of refunds	$ 8,358	$ 12,582