Investments AFS (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	$ 471,833	$ 1,734,380
Amount of short-term investments	353,284	1,351,054
Amount of long-term investments	118,549	383,326
Proceeds for sale of available-for-sale securities	1,501,500	273,900	$ 135,300
Realized gain on available-for-sale investments	13,727	18,469	$ 0
Corporate bonds and debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	1,000	926,929
Amount of corporate debt securities with no contractual maturity excluded from estimated fair value of available-for-sale securities		6,200
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	$ 2,203	$ 13,166