Fair Value Measurements (Details) (USD $) In Thousands	Jun. 30, 2011	Mar. 31, 2011
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	$ 249,433	$ 256,336
Level 1 [Member] | U.S. government and agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	175,863	174,331
Level 1 [Member] | International government agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	31,919	38,471
Level 1 [Member] | Corporate debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 1 [Member] | Strategic equity investments [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	793	675
Level 1 [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Cash equivalents	1,303	1,303
Total	209,878	214,780
Level 2 [Member] | U.S. government and agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 2 [Member] | International government agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 2 [Member] | Corporate debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	33,071	34,754
Level 2 [Member] | Strategic equity investments [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 2 [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Cash equivalents	0	0
Total	33,071	34,754
Level 3 [Member] | U.S. government and agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 3 [Member] | International government agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 3 [Member] | Corporate debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	728	1,047
Level 3 [Member] | Strategic equity investments [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	0	0
Level 3 [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Cash equivalents	0	0
Total	728	1,047
U.S. government and agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	175,863	174,331
International government agency debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	31,919	38,471
Corporate debt securities [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	33,799	35,801
Strategic equity investments [Member] | Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Measured on Recurring Basis Investments	793	675
Recurring [Member]
Summary of Company's assets measured at fair value on a recurring basis
Cash equivalents	1,303	1,303
Total	$ 243,677	$ 250,581