Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The amount of expense charged against earnings by an Entity to record deferred gains and losses on hedge instruments. Examples include gain on economic hedges, amortization of gain on designated fair value hedge and so forth.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Amount, after accumulated amortization, of debt discount.

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Amount of increase in the fair value of derivatives recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of decrease in the fair value of derivatives recognized in the income statement.

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Amount of unrealized gain (loss) recognized in the income statement for a financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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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	12 Months Ended
	Apr. 16, 2016	Dec. 31, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Jun. 26, 2014	Jun. 23, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Unamortized Discount						$ 553
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Loss on Derivative			$ 43,121	$ 38,569	$ 34,857
Derivative, Gain on Derivative			16,933	19,308	(25,414)
Interest Rate Swap [Member] \| Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amortization of Deferred Hedge Gains		$ 451	1,804	$ 1,353
2.7% Senior Notes [Member] \| Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Unamortized Discount			140
2.7% Senior Notes [Member] \| 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
3.95% Senior Notes [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Unamortized Discount						$ 458
3.95% Senior Notes [Member] \| Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Unamortized Discount			$ 286
Other Income [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)					2,137
Other Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)					$ (2,137)
US Treasury Interest Rate [Member] \| 2.7% Senior Notes [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Basis Spread on Variable Rate			0.00%
US Treasury Interest Rate [Member] \| 3.95% Senior Notes [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt Instrument, Basis Spread on Variable Rate			0.00%