Short-Term Borrowings and Long-Term Debt Interest Rate Swap - 2.7% Senior Notes due July 2019 (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 16, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016	Jun. 23, 2014
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Gain on Derivative		$ 5,265	$ 12,012	$ 16,767		$ 15,704
Derivative, Loss on Derivative		(10,550)	(12,307)	(30,447)		(18,083)
Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount							$ 250,000
Derivative, Gain on Derivative	$ 6,500
Amortization of Deferred Hedge Gains		$ 451		1,353
Interest Expense [Member] | Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Gain on Derivative			(3,151)	0		620
Derivative, Loss on Derivative			(1,177)	$ (764)		$ 0
Other Expense [Member] | Interest Rate Swap [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)					$ (1,354)
Other Income [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)			$ (3,151)		$ (1,354)