Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015			$ (34,365)
Foreign currency translation	$ (13,098)	$ (6,282)	(10,565)	$ (3,539)
Unrealized net gain on investments	(20,556)	13,344	(13,631)	30,642
Change in fair value of cash flow hedges	766	$ 2,785	2,855	3,619
Amount reclassified from AOCI			6,621	$ 7,298
Balance as of September 30, 2015	(55,706)		(55,706)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015			(59,170)
Foreign currency translation			$ (10,565)
Unrealized net gain on investments
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)			$ (10,565)
Balance as of September 30, 2015	(69,735)		(69,735)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015			$ 41,181
Foreign currency translation
Unrealized net gain on investments			$ (13,631)
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)			$ (13,631)
Balance as of September 30, 2015	27,550		27,550
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015			$ (15,235)
Foreign currency translation
Unrealized net gain on investments
Change in fair value of cash flow hedges			$ 9,476
Amount reclassified from AOCI			(6,621)
Other comprehensive income (loss)			2,855
Balance as of September 30, 2015	12,380		12,380
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015			$ (1,141)
Foreign currency translation
Unrealized net gain on investments
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)
Balance as of September 30, 2015	(1,141)		$ (1,141)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015			(34,365)
Foreign currency translation			(10,565)
Unrealized net gain on investments			(13,631)
Change in fair value of cash flow hedges			9,476
Amount reclassified from AOCI			(6,621)
Other comprehensive income (loss)			(21,341)
Balance as of September 30, 2015	$ (55,706)		$ (55,706)