Short- and Long-Term Investments and Investments on Deposit for Licensure (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	$ 1,462,324	$ 1,621,878
Gross Unrealized Holding Gains	32,247	22,022
Gross Unrealized Holding Losses	492	3,364
Fair value	1,494,079	1,640,536
Certificates of deposit [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	13,024	118,081
Gross Unrealized Holding Gains	0	13
Gross Unrealized Holding Losses	0	0
Fair value	13,024	118,094
Commercial paper [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	61,301	172,657
Gross Unrealized Holding Gains	132	2
Gross Unrealized Holding Losses	0	95
Fair value	61,433	172,564
Corporate bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	594,446	565,382
Gross Unrealized Holding Gains	5,086	2,852
Gross Unrealized Holding Losses	27	1,510
Fair value	599,505	566,724
Debt securities of government sponsored entities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	145,538	289,901
Gross Unrealized Holding Gains	625	742
Gross Unrealized Holding Losses	6	100
Fair value	146,157	290,543
Equity index funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	66,562	40,146
Gross Unrealized Holding Gains	6,217	1,355
Gross Unrealized Holding Losses	104	658
Fair value	72,675	40,843
Money market funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	87,752	15,067
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair value	87,752	15,067
Municipal bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	478,955	394,599
Gross Unrealized Holding Gains	20,123	16,978
Gross Unrealized Holding Losses	355	1,000
Fair value	498,723	410,577
U.S. Treasury securities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	14,746	26,045
Gross Unrealized Holding Gains	64	80
Gross Unrealized Holding Losses	0	1
Fair value	$ 14,810	$ 26,124

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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