Measured on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified							12 Months Ended				12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010	Mar. 31, 2013 Insurance Sector Auction Rate Securities	Mar. 31, 2012 Insurance Sector Auction Rate Securities	Mar. 31, 2013 Insurance Sector Auction Rate Securities Minimum	Mar. 31, 2013 Insurance Sector Auction Rate Securities Maximum	Mar. 31, 2013 Energy and Telecommunications Sector Insurance Sector Auction Rate Securities	Mar. 31, 2013 Student Loan Auction Rate Securities	Mar. 31, 2013 Student Loan, Energy, and Telecommunication Sector Auction Rate Securities Minimum	Mar. 31, 2013 Student Loan, Energy, and Telecommunication Sector Auction Rate Securities Maximum	Mar. 31, 2013 Fair Value, Inputs, Level 1 [Member]	Mar. 31, 2012 Fair Value, Inputs, Level 1 [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 2 [Member]	Mar. 31, 2012 Fair Value, Inputs, Level 2 [Member]	Mar. 31, 2013 Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2012 Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Fund Deposits Fair Value Disclosure	$ 100,878	$ 232,219											$ 100,878	$ 232,219	$ 0	$ 0	$ 0	$ 0
Marketable Equity Securities Fair Value Disclosure	5,509	5,264											5,509	5,264	0	0	0	0
Corporate Bonds and Debt Fair Value Disclosure	685,122	774,104											0	0	678,932	769,479	6,190	4,625
Government Agency Bonds Fair Value Disclosure	558,153	342,104											0	0	558,153	342,104	0	0
Cash Deposit Accounts Fair Value Disclosure	427,456	403,536											0	0	427,456	403,536	0	0
Municipal Bonds Fair Value Disclosure	25,138	20,122											0	0	25,138	20,122	0	0
Auction Rate Securities Fair Value Disclosure	33,791	10,246											0	0	0	0	33,791	10,246
Contingent consideration	19,100	0											0		0		19,100
Fair Value, Assets and Liabilities, as Classified on the Condensed Consolidated Balance Sheets [Abstract]
Cash and cash equivalents	528,334	635,755	703,924	492,130									100,878	232,219	427,456	403,536	0	0
Short-term investments	1,050,263	823,254											0	782	1,050,263	822,472	0	0
Long-term investments	257,450	328,586											5,509	4,482	211,960	309,233	39,981	14,871
Total assets measured at fair value	1,836,047	1,787,595											106,387	237,483	1,689,679	1,535,241	39,981	14,871
Liabilities, Fair Value Disclosure	19,100												0		0		19,100
Available-for-sale Securities, Other Disclosure Items [Abstract]
Value of auction rate securities for which recent auctions were unsuccessful					$ 9,800	$ 10,200			$ 5,300	$ 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											74.00%	99.00%
Probability of default											1.00%	14.00%