Measured on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified							3 Months Ended						3 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013 Insurance Sector Auction Rate Securities [Member]	Mar. 31, 2013 Insurance Sector Auction Rate Securities [Member]	Jun. 30, 2013 Insurance Sector Auction Rate Securities [Member] Minimum [Member]	Jun. 30, 2013 Insurance Sector Auction Rate Securities [Member] Maximum [Member]	Jun. 30, 2013 Energy And Telecommunications Sector Insurance Sector Auction Rate Securities [Member]	Mar. 31, 2013 Energy And Telecommunications Sector Insurance Sector Auction Rate Securities [Member]	Jun. 30, 2013 Student Loan Auction Rate Securities [Member]	Mar. 31, 2013 Student Loan Auction Rate Securities [Member]	Jun. 30, 2013 Student Loan, Energy, And Telecommunication Sector Auction Rate Securities [Member] Minimum [Member]	Jun. 30, 2013 Student Loan, Energy, And Telecommunication Sector Auction Rate Securities [Member] Maximum [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 1 [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 2 [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Fund Deposits Fair Value Disclosure	$ 168,699	$ 100,878													$ 168,699	$ 100,878	$ 0	$ 0	$ 0	$ 0
Marketable Equity Securities Fair Value Disclosure	5,931	5,509													5,931	5,509	0	0	0	0
Corporate Bonds and Debt Fair Value Disclosure	715,490	685,122													0	0	709,300	678,932	6,190	6,190
Government Agency Bonds Fair Value Disclosure	686,425	558,153													0	0	686,425	558,153	0	0
Cash Deposit Accounts Fair Value Disclosure	234,532	427,456													0	0	234,532	427,456	0	0
Municipal Bonds Fair Value Disclosure	49,574	25,138													0	0	49,574	25,138	0	0
Auction Rate Securities Fair Value Disclosure	34,599	33,791													0	0	0	0	34,599	33,791
Contingent consideration	20,492	19,100													0	0	0	0	20,492	19,100
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	403,231	528,334	779,848	635,755											168,699	100,878	234,532	427,456	0	0
Short-term investments	558,644	1,050,263													0	0	558,644	1,050,263	0	0
Long-term investments	933,375	257,450													5,931	5,509	886,655	211,960	40,789	39,981
Total assets measured at fair value	1,895,250	1,836,047													174,630	106,387	1,679,831	1,689,679	40,789	39,981
Liabilities, Fair Value Disclosure	20,492	19,100													0	0	0	0	20,492	19,100
Available-for-sale Securities, Other Disclosure Items [Abstract]
Value of auction rate securities for which recent auctions were unsuccessful					$ 9,800	$ 9,800			$ 5,300	$ 5,300	$ 19,400	$ 18,700
Discount rate							2.00%	2.50%					0.00%	0.00%
Liquidity risk premium (percentage)							9.10%	29.50%					3.00%	5.00%
Anticipated liquidity horizon							7 years	10 years
Cumulative probability of principal being returned prior to maturity													73.00%	99.00%
Fair Value Inputs, Probability of Default													1.00%	12.00%