Accumulated Other Comprehensive Income (Loss) Components of Net of Tax (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2014			$ (53,923)
Foreign currency translation	(6,282)	1,557	(3,539)	(2,205)
Unrealized net gain on investments	13,344	(26,773)	30,642	(26,752)
Change in fair value of cash flow hedges			(3,679)
Amount reclassified from AOCI			7,298	8,685
Other comprehensive income (loss)			30,722
Balance as of September 30, 2014	(23,201)		(23,201)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2014			(39,287)
Foreign currency translation			(3,539)
Unrealized net gain on investments			0
Change in fair value of cash flow hedges			0
Amount reclassified from AOCI			0
Other comprehensive income (loss)			(3,539)
Balance as of September 30, 2014	(42,826)		(42,826)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2014			5,991
Foreign currency translation			0
Unrealized net gain on investments			30,642
Change in fair value of cash flow hedges			0
Amount reclassified from AOCI			0
Other comprehensive income (loss)			30,642
Balance as of September 30, 2014	36,633		36,633
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2014			(20,321)
Foreign currency translation			0
Unrealized net gain on investments			0
Change in fair value of cash flow hedges			(3,679)
Amount reclassified from AOCI			7,298
Other comprehensive income (loss)			3,619
Balance as of September 30, 2014	(16,702)		(16,702)
Postretirement Benefit Obligation Net Loss [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2014			(306)
Foreign currency translation			0
Unrealized net gain on investments			0
Change in fair value of cash flow hedges			0
Amount reclassified from AOCI			0
Other comprehensive income (loss)			0
Balance as of September 30, 2014	$ (306)		$ (306)