Short- and Long-Term Investments and Investments on Deposit for Licensure (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	$ 1,377,711	$ 1,621,878
Gross Unrealized Holding Gains	23,580	22,022
Gross Unrealized Holding Losses	1,230	3,364
Fair value	1,400,061	1,640,536
Certificates of deposit [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	13,019	118,081
Gross Unrealized Holding Gains	0	13
Gross Unrealized Holding Losses	0	0
Fair value	13,019	118,094
Commercial paper [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	51,685	172,657
Gross Unrealized Holding Gains	77	2
Gross Unrealized Holding Losses	0	95
Fair value	51,762	172,564
Corporate bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	572,785	565,382
Gross Unrealized Holding Gains	3,441	2,852
Gross Unrealized Holding Losses	163	1,510
Fair value	576,063	566,724
Debt Securities of Government Sponsored Entities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	219,432	289,901
Gross Unrealized Holding Gains	616	742
Gross Unrealized Holding Losses	80	100
Fair value	219,968	290,543
Equity index funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	60,889	40,146
Gross Unrealized Holding Gains	3,355	1,355
Gross Unrealized Holding Losses	394	658
Fair value	63,850	40,843
Money market funds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	60,105	15,067
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair value	60,105	15,067
Municipal bonds [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	379,855	394,599
Gross Unrealized Holding Gains	16,029	16,978
Gross Unrealized Holding Losses	591	1,000
Fair value	395,293	410,577
U.S. Treasury securities [Member]
Reconciliation schedule of available-for-sale securities from cost basis to fair value
Amortized Cost	19,941	26,045
Gross Unrealized Holding Gains	62	80
Gross Unrealized Holding Losses	2	1
Fair value	$ 20,001	$ 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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