Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Cash flows from operating activities:
Net income	$ 61,071	$ 85,386
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	7,420	6,842
Provision for doubtful accounts	15,601	12,667
Deferred income taxes	(3,742)	(2,685)
Excess tax benefit from stock option exercises	(805)	(351)
Stock-based compensation expense	4,483	3,914
Other	(339)	(1,430)
Changes in operating assets and liabilities:
Restricted cash	1,005	(1,565)
Accounts receivable	(21,906)	(3,528)
Accounts payable	(1,212)	4,769
Other operating assets and liabilities	22,166	56,922
Deferred revenue	(46,396)	21,178
Net cash flows from operating activities	37,346	182,119
Cash flows from investing activities:
Facility expenditures and land purchases	(132)	(502)
Capital expenditures, net	(4,518)	(4,699)
Proceeds from sales and maturities of investments and repayment of notes	98,955	142,085
Purchase of investments and note advances	(63,545)	(158,589)
Net cash flows from investing activities	30,760	(21,705)
Cash flows from financing activities:
Excess tax benefit from stock option exercises	805	351
Proceeds from exercise of stock options	4,668	3,028
Debt issue costs	(1,525)	0
Proceeds from revolving borrowings	175,000	0
Repayment of revolving borrowings	(150,000)	0
Repurchase of common stock and shares tendered for taxes	(147,571)	(139,650)
Net cash flows from financing activities	(118,623)	(136,271)
Net change in cash and cash equivalents	(50,517)	24,143
Cash and cash equivalents at beginning of period	228,993	163,779
Cash and cash equivalents at end of period	$ 178,476	$ 187,922