Investments AFS (Details) (USD $)	Mar. 31, 2014	Mar. 31, 2013
Investments [Abstract]
Amount of short-term investments	$ 878,182,000	$ 1,050,263,000
Amount of long-term investments	798,712,000	257,450,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	782,700,000
Amount of corporate debt securities with no contractual maturity excluded from estimated fair value of available-for-sale securities	$ 6,200,000	$ 6,200,000