Short-Term Borrowings and Long-Term Debt 5.45% Junior Subordinated Notes (Details) - Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] - USD ($) $ in Thousands	Mar. 31, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,250,000
5.45% Junior Subordinated Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500,000	$ 500,000