Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities:
Net income	$ 67,318	$ 93,177	$ 231,704	$ 276,668
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	6,486	6,205	20,368	19,687
Provision for doubtful accounts	13,864	22,151	44,018	67,950
Deferred income taxes	(5,831)	(6,568)	(13,008)	(16,031)
Excess tax benefit from stock option exercises	(167)	(1,313)	(1,145)	(3,253)
Stock-based compensation expense	4,166	3,708	12,838	12,707
Other	(820)	268	(3,237)	758
Changes in operating assets and liabilities:
Restricted cash	(26)	(38)	(158)	1,783
Accounts receivable	(22,963)	(9,007)	(31,221)	(67,770)
Accounts payable	22,817	3,504	20,905	18,345
Other operating assets and liabilities	5,035	6,756	29,071	29,096
Deferred revenue	(40,801)	(1,939)	(18,316)	23,235
Net cash flows from operating activities	49,078	116,904	291,819	363,175
Cash flows from investing activities:
Facility expenditures and land purchases	(1,454)	(1,775)	(3,129)	(4,368)
Capital expenditures, net	(7,827)	(8,090)	(20,013)	(20,629)
Proceeds from sales and maturities of investments and repayment of notes	52,317	81,517	312,709	281,343
Purchase of investments and note advances	(48,613)	(100,741)	(330,306)	(323,515)
Net cash flows from investing activities	(5,577)	(29,089)	(40,739)	(67,169)
Cash flows from financing activities:
Excess tax benefit from stock option exercises	167	1,313	1,145	3,253
Proceeds from exercise of stock options	303	5,210	5,286	7,830
Repurchase of common stock and shares tendered for taxes	(29,629)	(114,906)	(248,713)	(315,921)
Net cash flows from financing activities	(29,159)	(108,383)	(242,282)	(304,838)
Net change in cash and cash equivalents	14,342	(20,568)	8,798	(8,832)
Cash and cash equivalents at beginning of period	158,235	140,524	163,779	128,788
Cash and cash equivalents at end of period	$ 172,577	$ 119,956	$ 172,577	$ 119,956