Short-Term Borrowings and Long-Term Debt Interest Rate Swap - Revolving Credit Facility (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016	Jun. 23, 2014
Line of Credit Facility [Line Items]
Derivative, Term of Contract				4 years 245 days
Revolving Credit Facility [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Fixed Interest Rate			2.30%
Derivative, Notional Amount			$ 500,000
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax			(2,249)
Deferred Tax Assets, Hedging Transactions			1,413
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative	$ 10,550	$ 12,307		$ 30,447		$ 18,083
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Notional Amount							$ 250,000
Cash Flow Hedging [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative				4,426
Other Nonoperating Income (Expense) [Member] | Cash Flow Hedging [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative			$ 3,662	3,662	$ 0
Interest Expense [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative, Loss on Derivative		$ 1,177		$ 764		$ 0