Derivatives Derivatives, Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2016		Dec. 31, 2015
Derivative [Line Items]
Derivative, Notional Amount	$ 8,080,000		$ 9,680,000
Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	1,355,000	[1]	2,955,000
Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	425,000		$ 425,000
12 months or less | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 185,000
Derivative, Average Fixed Interest Rate	0.92%
12 months or less | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
13-24 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
13-24 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
25-36 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 160,000
Derivative, Average Fixed Interest Rate	1.37%
25-36 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
37-48 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 335,000
Derivative, Average Fixed Interest Rate	1.61%
37-48 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 250,000
Derivative, Average Fixed Interest Rate	1.91%
49-60 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 50,000
Derivative, Average Fixed Interest Rate	1.35%
49-60 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 150,000
Derivative, Average Fixed Interest Rate	1.71%
61-72 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
61-72 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
73-84 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
73-84 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
85-96 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
85-96 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%
97-108 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 375,000
Derivative, Average Fixed Interest Rate	2.83%
97-108 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 25,000
Derivative, Average Fixed Interest Rate	2.71%
109-120 months | Pay-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 250,000
Derivative, Average Fixed Interest Rate	2.43%
109-120 months | Receive-fixed interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 0
Derivative, Average Fixed Interest Rate	0.00%

[1] The notional amount of pay-fixed interest rate swaps that were forward starting as of June 30, 2016 was $625,000.