Provision for Taxes (Narratives) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating losses potentially not utilized	$ 45,300
Federal statutory rate, blended rate for fiscal year	31.55%
Provisional benefit amount	$ 355,700
Deferred tax assets, effect of Tax Cuts and Jobs Act, tax expense (benefit)	371,500
Reclassified amount from accumulated other comprehensive income to retained earnings	8,700
Provisional tax expense for foreign tax credits	11,700
Phase three tax, increase in income tax expense	4,000
Unrecognized tax benefits	35,739	26,720	$ 23,912
Revaluation based on change in after tax benefit	5,755
Tax expense (net of settlements)	3,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Unrecognized tax benefits, income tax penalties and interest expense	400
Change in federal tax rate, benefit amount		1,400
Unrecognized tax benefits, income tax penalties and interest accrued	$ 8,500	$ 6,700