Short- and Long-Term Investments and Investments on Deposit for Licensure (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	$ 1,621,878	$ 983,004
Gross Unrealized Holding Gains	22,022	4,585
Gross Unrealized Holding Losses	3,364	3,578
Fair value	1,640,536	984,011
Auction Rate Securities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	12,550	22,650
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	999	1,357
Fair value	11,551	21,293
Certificates of Deposit [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	118,081	13,651
Gross Unrealized Holding Gains	13	0
Gross Unrealized Holding Losses	0	0
Fair value	118,094	13,651
Commercial paper [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	172,657	14,797
Gross Unrealized Holding Gains	2	0
Gross Unrealized Holding Losses	95	4
Fair value	172,564	14,793
Corporate Bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	565,382	235,775
Gross Unrealized Holding Gains	2,852	2,327
Gross Unrealized Holding Losses	1,510	186
Fair value	566,724	237,916
Debt Securities of Government Sponsored Entities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	289,901	331,893
Gross Unrealized Holding Gains	742	623
Gross Unrealized Holding Losses	100	465
Fair value	290,543	332,051
Equity index funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	40,146
Gross Unrealized Holding Gains	1,355
Gross Unrealized Holding Losses	658
Fair value	40,843
Federally insured corporate bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost		21,097
Gross Unrealized Holding Gains		360
Gross Unrealized Holding Losses		3
Fair value		21,454
Money market funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	15,067	20,315
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair value	15,067	20,315
Municipal bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	382,049	301,234
Gross Unrealized Holding Gains	16,978	1,145
Gross Unrealized Holding Losses	1	1,562
Fair value	399,026	300,817
U.S. Treasury securities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	26,045	21,592
Gross Unrealized Holding Gains	80	130
Gross Unrealized Holding Losses	1	1
Fair value	$ 26,124	$ 21,721

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details