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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The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
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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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Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of net gain (loss) recognized in earnings when a hedged firm commitment no longer qualifies as a fair value hedge.

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-Name Accounting Standards Codification
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- Definition

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

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Derivatives and Hedging Instruments - Narrative (Details) £ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Jun. 30, 2019 USD ($) instrument	Jun. 30, 2018 USD ($)	Jun. 30, 2019 GBP (£) instrument
Forward contracts
Derivative [Line Items]
Net derivative gain (loss) included in OCI expected to be reclassified into earnings		$ 1,200,000
Gains or losses were reclassified from OCI into earnings		0	$ 0
Forward contracts \| Derivatives Designated as Hedging Instruments
Derivative [Line Items]
Derivative instrument, notional amount		28,800,000
Interest rate swap agreements \| Cash Flow Hedging
Derivative [Line Items]
Derivative instrument, notional amount		$ 368,100,000
Number of interest rate derivative held \| instrument		6		6
Interest rate cap contracts
Derivative [Line Items]
Derivative instrument, notional amount		$ 444,500,000		£ 350.0
Interest rate cap contracts \| Cash Flow Hedging
Derivative [Line Items]
Number of interest rate derivative held \| instrument		2		2
Minimum \| Not Designated as Hedging Instrument \| Cash Flow Hedging
Derivative [Line Items]
Term of contract (years)	1 month
Maximum \| Not Designated as Hedging Instrument \| Cash Flow Hedging
Derivative [Line Items]
Term of contract (years)		3 months