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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
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Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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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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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Number of credit risk derivative instruments held.

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Number of interest rate derivative instruments held by the entity at the reporting date.

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Significant Accounting Policies - Derivative Financial Instruments (Details) € in Millions, $ in Millions	Mar. 31, 2017 EUR (€) item	Mar. 31, 2017 USD ($) item	Dec. 31, 2016 EUR (€) item	Dec. 31, 2016 USD ($) item
Derivative Financial Instruments
Number of credit-risk-related hedging or derivative activities \| item	0	0
Gross accumulated other comprehensive income related to derivative activities		$ 36.3		$ 35.0
Interest rate swap \| Designated as Hedging Instrument
Derivative Financial Instruments
Number of Instruments \| item	1	1	1	1
Notional Amount		$ 250.0		$ 250.0
Interest rate swap \| Deferred costs and other assets \| Designated as Hedging Instrument
Derivative Financial Instruments
Interest rate derivative asset, fair value		21.1		21.1
Euro-USD currency forward contract \| August 11, 2017 \| Designated as Hedging Instrument
Derivative Financial Instruments
Notional Amount \| €	€ 50.0		€ 50.0
Forward contract net, fair value		15.1		15.5
Euro-USD currency forward contract \| May 15, 2019 \| Designated as Hedging Instrument
Derivative Financial Instruments
Notional Amount \| €	50.0		50.0
Forward contract net, fair value		3.6		3.9
Euro-USD currency forward contract \| May 15, 2019 \| Designated as Hedging Instrument
Derivative Financial Instruments
Notional Amount \| €	50.0		50.0
Forward contract net, fair value		1.2		1.5
Euro-USD currency forward contract \| May 15, 2020 \| Designated as Hedging Instrument
Derivative Financial Instruments
Notional Amount \| €	50.0		50.0
Forward contract net, fair value		0.9		1.1
Euro-USD currency forward contract \| May 14, 2021 \| Designated as Hedging Instrument
Derivative Financial Instruments
Notional Amount \| €	€ 50.0		€ 50.0
Forward contract net, fair value		$ 0.4		$ 0.6