Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax
Balance as of March 31, 2016			$ (60,525)
Foreign currency translation	$ (5,821)	$ (6,727)	(7,803)	$ (17,292)
Unrealized net gain on investments	2,755	666	42,156	(12,965)
Change in fair value of cash flow hedges	1,922	2,699	5,138	5,554
Amount reclassified from AOCI			6,940	9,736
Other comprehensive income (loss)	64,084	$ 78,407	428,367	$ 411,730
Balance as of December 31, 2016	(21,034)		(21,034)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax
Balance as of March 31, 2016			(63,643)
Foreign currency translation			(7,803)
Unrealized net gain on investments
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)			(7,803)
Balance as of December 31, 2016	(71,446)		(71,446)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax
Balance as of March 31, 2016			14,115
Foreign currency translation
Unrealized net gain on investments			42,156
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)			42,156
Balance as of December 31, 2016	56,271		56,271
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax
Balance as of March 31, 2016			(9,208)
Foreign currency translation
Unrealized net gain on investments
Change in fair value of cash flow hedges			12,078
Amount reclassified from AOCI			(6,940)
Other comprehensive income (loss)			5,138
Balance as of December 31, 2016	(4,070)		(4,070)
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax
Balance as of March 31, 2016			(1,789)
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 December 31, 2016	(1,789)		(1,789)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax
Balance as of March 31, 2016			(60,525)
Foreign currency translation			(7,803)
Unrealized net gain on investments			42,156
Change in fair value of cash flow hedges			12,078
Amount reclassified from AOCI			(6,940)
Other comprehensive income (loss)			39,491
Balance as of December 31, 2016	$ (21,034)		$ (21,034)