Significant Accounting Policies Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Schedule of Income Tax Expense [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	$ 4,549	$ 7,325	$ 3,303
Income Tax Expense (Benefit)	$ 20,561	$ (102,510)	$ 84,175
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	31.50%	35.00%
Domestic Tax Authority [Member]
Schedule of Income Tax Expense [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%	21.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		$ 220,935