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

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Derivative, Variable Interest Rate, Term

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Represents the weighted average interest rate paid related to derivatives.

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Represents the weighted average interest rate received related to derivatives.

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Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Average fixed interest rate related to the group of interest rate derivatives.

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Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Average variable interest rate related to the group of interest rate derivatives.

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The number of derivative instruments of a particular group held by the entity.

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Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of the cost of borrowed funds accounted for as interest expense.

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The carrying amount, as of the date of the latest financial statement presented, of all assets that are pledged as collateral for the payment of the related debt obligation primarily arising from secured borrowings, repurchase agreements or other current or potential obligations, where the secured party does not have the right by contract or custom to sell or re-pledge the collateral and therefore are not reclassified and separately reported in the statement of financial position.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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Other Assets (Derivative Instruments) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) derivative	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) derivative	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Assets pledged	$ 7,237,814		$ 7,237,814		$ 8,145,197
Interest expense attributable to Swaps	51,810	$ 49,022	102,364	$ 99,371
AOCI from derivative hedging instruments:
Balance at beginning of period	8,245	(34,824)	(11,424)	(46,721)
Net gain/(loss) on Swaps	7,915	(1,017)	27,584	10,880
Balance at end of period	16,160	(35,841)	16,160	(35,841)
Interest Rate Contract
Derivative [Line Items]
Assets pledged	3,097		3,097		28,161
Interest Rate Contract \| Agency MBS, at fair value
Derivative [Line Items]
Assets pledged	3,097		3,097		21,756
Interest Rate Contract \| Restricted cash
Derivative [Line Items]
Assets pledged	0		0		6,405
Swaps, at fair value
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 2,600,000		$ 2,600,000		$ 2,550,000
Weighted average fixed-pay rate	2.07%		2.07%		2.04%
Weighted Average Variable Interest Rate	2.08%		2.08%		1.50%
Interest expense attributable to Swaps	$ 808	$ 6,488	$ 3,640	$ 14,297
Weighted average Swap rate paid	2.05%	1.98%	2.04%	1.93%
Weighted average Swap rate received	1.92%	1.01%	1.76%	0.90%
Swaps, at fair value \| Within 30 days
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 500,000		$ 500,000		$ 0
Weighted average fixed-pay rate	1.50%		1.50%		0.00%
Weighted Average Variable Interest Rate	2.06%		2.06%		0.00%
Swaps, at fair value \| Over 30 days to 3 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 0		$ 0		$ 0
Weighted average fixed-pay rate	0.00%		0.00%		0.00%
Weighted Average Variable Interest Rate	0.00%		0.00%		0.00%
Swaps, at fair value \| Over 3 months to 6 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 0		$ 0		$ 50,000
Weighted average fixed-pay rate	0.00%		0.00%		1.45%
Weighted Average Variable Interest Rate	0.00%		0.00%		1.56%
Swaps, at fair value \| Over 6 months to 12 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 200,000		$ 200,000		$ 500,000
Weighted average fixed-pay rate	1.71%		1.71%		1.50%
Weighted Average Variable Interest Rate	2.09%		2.09%		1.46%
Swaps, at fair value \| Over 12 months to 24 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 200,000		$ 200,000		$ 200,000
Weighted average fixed-pay rate	2.05%		2.05%		1.71%
Weighted Average Variable Interest Rate	2.10%		2.10%		1.54%
Swaps, at fair value \| Over 24 months to 36 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 1,600,000		$ 1,600,000		$ 1,500,000
Weighted average fixed-pay rate	2.25%		2.25%		2.22%
Weighted Average Variable Interest Rate	2.09%		2.09%		1.51%
Swaps, at fair value \| Over 36 months to 48 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 0		$ 0		$ 200,000
Weighted average fixed-pay rate	0.00%		0.00%		2.20%
Weighted Average Variable Interest Rate	0.00%		0.00%		1.53%
Swaps, at fair value \| Over 48 months to 60 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 0		$ 0		$ 0
Weighted average fixed-pay rate	0.00%		0.00%		0.00%
Weighted Average Variable Interest Rate	0.00%		0.00%		0.00%
Swaps, at fair value \| Over 60 months to 72 months
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 100,000		$ 100,000		$ 100,000
Weighted average fixed-pay rate	2.75%		2.75%		2.75%
Weighted Average Variable Interest Rate	2.09%		2.09%		1.50%
Swaps, at fair value \| July 2023, Derivative Maturity
Derivative [Line Items]
Number of instruments held \| derivative	1		1
Swaps, at fair value \| Designated as Hedging Instrument
Derivative [Line Items]
Aggregate notional amount of derivatives	$ 2,600,000		$ 2,600,000
Average maturity term of swaps			22 months
Swaps, at fair value \| Minimum \| LIBOR
Derivative [Line Items]
Derivative, variable interest rate, term			1 month
Swaps, at fair value \| Maximum \| Designated as Hedging Instrument
Derivative [Line Items]
Maximum maturity term of swaps			62 months
Swaps, at fair value \| Maximum \| LIBOR
Derivative [Line Items]
Derivative, variable interest rate, term			3 months