Short- and Long-Term Investments and Investments on Deposit for Licensure (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	$ 1,243,461	$ 983,004
Gross Unrealized Holding Gains	11,377	4,585
Gross Unrealized Holding Losses	1,788	3,578
Fair value	1,253,050	984,011
Auction Rate Securities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	16,750	22,650
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	1,078	1,357
Fair value	15,672	21,293
Certificates of Deposit [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	7,002	13,651
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair value	7,002	13,651
Commercial paper [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	51,268	14,797
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	6	4
Fair value	51,262	14,793
Corporate Bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	343,337	235,775
Gross Unrealized Holding Gains	2,917	2,327
Gross Unrealized Holding Losses	75	186
Fair value	346,179	237,916
Debt Securities of Government Sponsored Entities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	374,866	331,893
Gross Unrealized Holding Gains	776	623
Gross Unrealized Holding Losses	198	465
Fair value	375,444	332,051
Equity Index Funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	15,888
Gross Unrealized Holding Gains	329
Gross Unrealized Holding Losses	0
Fair value	16,217
Federally insured corporate bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	21,045	21,097
Gross Unrealized Holding Gains	185	360
Gross Unrealized Holding Losses	0	3
Fair value	21,230	21,454
Money market funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	23,791	20,315
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair value	23,791	20,315
Municipal bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	355,121	301,234
Gross Unrealized Holding Gains	7,065	1,145
Gross Unrealized Holding Losses	431	1,562
Fair value	361,755	300,817
U.S. Treasury securities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	34,393	21,592
Gross Unrealized Holding Gains	105	130
Gross Unrealized Holding Losses	0	1
Fair value	$ 34,498	$ 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.

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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.

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- 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.

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