Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2019	$ (66,698)
Foreign currency translation	2,982	$ (2,093)
Unrealized net gain on investments	40,788	(39,672)
Change in fair value of cash flow hedges		422
Amount reclassified from AOCI	3	516
Balance as of June 30, 2019	(23,873)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2019	(56,612)
Foreign currency translation	2,982
Unrealized net gain on investments	0
Change in fair value of cash flow hedges	0
Other comprehensive income (loss)	(2,093)
Balance as of June 30, 2019	(58,705)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2019	(7,259)
Foreign currency translation	0
Unrealized net gain on investments	40,788
Change in fair value of cash flow hedges	0
Other comprehensive income (loss)	40,788
Balance as of June 30, 2019	33,529
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2019	107
Foreign currency translation	0
Unrealized net gain on investments	0
Change in fair value of cash flow hedges	(945)
Other comprehensive income (loss)	(945)
Balance as of June 30, 2019	(838)
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2019	(2,934)
Foreign currency translation	0	0
Unrealized net gain on investments	0	0
Change in fair value of cash flow hedges	0	0
Other comprehensive income (loss)	0
Balance as of June 30, 2019	(2,934)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2019	(66,698)
Foreign currency translation	2,982	(2,093)
Unrealized net gain on investments	40,788	(39,672)
Change in fair value of cash flow hedges	(945)	$ 422
Other comprehensive income (loss)	42,825
Balance as of June 30, 2019	$ (23,873)

A roll forward schedule of the summary of accumulated other comprehensive income (loss) components, net of tax.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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