CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Cash flows from operating activities:
Net income	$ 46,002	$ 79,000	$ 107,073	$ 164,386
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	7,695	7,040	15,115	13,882
Provision for doubtful accounts	19,006	17,487	34,607	30,154
Deferred income taxes	(6,334)	(4,492)	(10,076)	(7,177)
Excess tax benefit from stock option exercises	(574)	(627)	(1,379)	(978)
Stock-based compensation expense	4,272	4,758	8,755	8,672
Other	96	(987)	(243)	(2,417)
Changes in operating assets and liabilities:
Restricted cash	372	1,433	1,377	(132)
Accounts receivable	(38,270)	(4,730)	(60,176)	(8,258)
Accounts payable	3,113	(6,681)	1,901	(1,912)
Other operating assets and liabilities	(15,400)	(32,886)	6,766	24,036
Deferred revenue	(58,274)	1,307	(104,670)	22,485
Net cash flows from operating activities	(38,296)	60,622	(950)	242,741
Cash flows from investing activities:
Facility expenditures and land purchases	(253)	(1,173)	(385)	(1,675)
Capital expenditures, net	(7,117)	(7,487)	(11,635)	(12,186)
Proceeds from sales and maturities of investments and repayment of notes	117,216	118,307	216,171	260,392
Purchase of investments and note advances	0	(123,104)	(63,545)	(281,693)
Net cash flows from investing activities	109,846	(13,457)	140,606	(35,162)
Cash flows from financing activities:
Excess tax benefit from stock option exercises	574	627	1,379	978
Proceeds from exercise of stock options	3,423	1,955	8,091	4,983
Debt issue costs	0	0	(1,525)	0
Proceeds from revolving borrowings	0	0	175,000	0
Repayment of revolving borrowings	(25,000)	0	(175,000)	0
Repurchase of common stock and shares tendered for taxes	(61,789)	(79,434)	(209,360)	(219,084)
Net cash flows from financing activities	(82,792)	(76,852)	(201,415)	(213,123)
Net change in cash and cash equivalents	(11,242)	(29,687)	(61,759)	(5,544)
Cash and cash equivalents at beginning of period	178,476	187,922	228,993	163,779
Cash and cash equivalents at end of period	$ 167,234	$ 158,235	$ 167,234	$ 158,235