Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2017	$ (51,236)
Foreign currency translation	8,267	$ (278)
Unrealized net gain on investments	6,911	19,388
Change in fair value of cash flow hedges	960	1,290
Amount reclassified from AOCI	1,550	$ 2,809
Balance as of June 30, 2017	(35,098)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2017	(69,505)
Foreign currency translation	8,267
Unrealized net gain on investments
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)	8,267
Balance as of June 30, 2017	(61,238)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2017	23,099
Foreign currency translation
Unrealized net gain on investments	6,911
Change in fair value of cash flow hedges
Amount reclassified from AOCI
Other comprehensive income (loss)	6,911
Balance as of June 30, 2017	30,010
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2017	(3,059)
Foreign currency translation
Unrealized net gain on investments
Change in fair value of cash flow hedges	2,510
Amount reclassified from AOCI	(1,550)
Other comprehensive income (loss)	960
Balance as of June 30, 2017	(2,099)
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2017	(1,771)
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, 2017	(1,771)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2017	(51,236)
Foreign currency translation	8,267
Unrealized net gain on investments	6,911
Change in fair value of cash flow hedges	2,510
Amount reclassified from AOCI	(1,550)
Other comprehensive income (loss)	16,138
Balance as of June 30, 2017	$ (35,098)