Fair Values of Assets and Liabilities Unrealized and Realized Gain (Loss) on Trading Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ (34,793)	$ 9,382	$ (25,246)	$ 32,184
Trading Securities, Unrealized Holding Gain	$ (38,741)	$ 5,975	$ (51,313)	$ 16,115