Investments AFS, Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in a continuous unrealized loss position, less than twelve months		$ 148,562
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, less than twelve months		(99)
Fair value of available-for-sale securities in a continuous unrealized loss position, greater than twelve months		1,000
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, greater than twelve months		0
Fair value of available-for-sale securities in a continuous unrealized loss position		149,562
Accumulated loss, available-for-sale securities in a continuous unrealized loss position		(99)
Marketable equity securities
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in a continuous unrealized loss position, less than twelve months	$ 1,266
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, less than twelve months	(895)
Fair value of available-for-sale securities in a continuous unrealized loss position, greater than twelve months	0
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, greater than twelve months	0
Fair value of available-for-sale securities in a continuous unrealized loss position	1,266
Accumulated loss, available-for-sale securities in a continuous unrealized loss position	$ (895)
Government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in a continuous unrealized loss position, less than twelve months		148,562
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, less than twelve months		(99)
Fair value of available-for-sale securities in a continuous unrealized loss position, greater than twelve months		0
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, greater than twelve months		0
Fair value of available-for-sale securities in a continuous unrealized loss position		148,562
Accumulated loss, available-for-sale securities in a continuous unrealized loss position		(99)
Corporate bonds and debt
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale securities in a continuous unrealized loss position, less than twelve months		0
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, less than twelve months		0
Fair value of available-for-sale securities in a continuous unrealized loss position, greater than twelve months		1,000
Accumulated loss, available-for-sale securities in a continuous unrealized loss position, greater than twelve months		0
Fair value of available-for-sale securities in a continuous unrealized loss position		1,000
Accumulated loss, available-for-sale securities in a continuous unrealized loss position		$ 0