Short-Term Borrowings and Long-Term Debt Line of Credit (Details) - USD ($) $ in Thousands	9 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2016
Line of Credit Facility [Line Items]
Line of Credit Facility, Annual Principal Payment	$ 500,000
Line of Credit Facility, Increase (Decrease), Net	460,000
Line of Credit Facility, Fair Value of Amount Outstanding			$ 40,000
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross	2,250,000
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | 5.45% Junior Subordinated Notes [Member]
Line of Credit Facility [Line Items]
Long-term Debt, Gross	$ 500,000	$ 500,000