Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2015	$ (34,365)
Foreign currency translation	2,533	$ 2,743
Unrealized net gain on investments	6,925	17,298
Change in fair value of cash flow hedges	2,089	834
Amount reclassified from AOCI	3,360	$ 3,647
Balance as of June 30, 2015	(22,818)
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	$ 2,533
Unrealized net gain on investments
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)	$ 2,533
Balance as of June 30, 2015	(56,637)
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	$ 6,925
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)	$ 6,925
Balance as of June 30, 2015	48,106
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	$ 5,449
Amount reclassified from AOCI	(3,360)
Other comprehensive income (loss)	2,089
Balance as of June 30, 2015	(13,146)
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 June 30, 2015	$ (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	2,533
Unrealized net gain on investments	6,925
Change in fair value of cash flow hedges	5,449
Amount reclassified from AOCI	(3,360)
Other comprehensive income (loss)	11,547
Balance as of June 30, 2015	$ (22,818)