Investments AFS (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015
Investments [Abstract]
Amount of short-term investments	$ 969,003		$ 1,351,054
Amount of long-term investments	898,024		$ 383,326
Carrying value of available-for-sale investment previously classified as non-marketable cost-method investment	3,600
Proceeds for sale of available-for-sale securities	89,200	$ 144,000
Realized gain on available-for-sale investments	13,959	$ 0
Amount of corporate debt securities with no contractual maturity excluded from estimated fair value of available-for-sale securities	$ 6,200