CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income	$ 174,804	$ 159,638
Adjustments to reconcile net income to net cash provided from operating activities:
Depreciation and amortization	22,725	18,026
Accretion of contingent consideration liabilities	763	817
Stock-based compensation expense	20,441	20,037
Deferred income taxes	16,731	5,554
Changes in assets and liabilities:
Accounts receivable	(20,119)	(25,665)
Prepaid expenses and other assets	1,789	(5,026)
Other assets	754	4,021
Accounts payable and accrued expenses	(14,699)	(13,182)
Income taxes payable	(158)	1,738
Long-term professional liabilities	14,063	11,907
Other liabilities	2,641	3,056
Net cash provided from operating activities	219,735	180,921
Cash flows from investing activities:
Acquisition payments, net of cash acquired	(202,362)	(79,928)
Purchases of investments	(21,099)	(26,039)
Proceeds from maturities of investments	23,963	28,585
Purchases of property and equipment	(9,947)	(28,622)
Net cash used in investing activities	(209,445)	(106,004)
Cash flows from financing activities:
Borrowings on line of credit	401,500	387,500
Payments on line of credit	(382,500)	(484,000)
Payment of contingent consideration liabilities	(4,903)	(3,700)
Payments on capital lease obligations	(121)	(413)
Excess tax benefit from exercises of stock options and vesting of restricted stock	4,435	6,886
Proceeds from issuance of common stock	18,827	28,308
Net cash provided from (used in) financing activities	37,238	(65,419)
Net increase in cash and cash equivalents	47,528	9,498
Cash and cash equivalents at beginning of period	18,596	26,251
Cash and cash equivalents at end of period	$ 66,124	$ 35,749