Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2016	$ (60,525)
Foreign currency translation	(278)	$ 2,533
Unrealized net gain on investments	19,388	6,925
Change in fair value of cash flow hedges	1,290	2,089
Amount reclassified from AOCI	2,809	$ 3,360
Balance as of June 30, 2016	(40,125)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2016	(63,643)
Foreign currency translation	(278)
Unrealized net gain on investments
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)	(278)
Balance as of June 30, 2016	(63,921)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2016	14,115
Foreign currency translation
Unrealized net gain on investments	19,388
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)	19,388
Balance as of June 30, 2016	33,503
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2016	(9,208)
Foreign currency translation
Unrealized net gain on investments
Change in fair value of cash flow hedges	4,099
Amount reclassified from AOCI	(2,809)
Other comprehensive income (loss)	1,290
Balance as of June 30, 2016	(7,918)
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
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 June 30, 2016	(1,789)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2016	(60,525)
Foreign currency translation	(278)
Unrealized net gain on investments	19,388
Change in fair value of cash flow hedges	4,099
Amount reclassified from AOCI	(2,809)
Other comprehensive income (loss)	20,400
Balance as of June 30, 2016	$ (40,125)