Offsetting of Assets and Liabilities (Details) - USD ($) $ in Thousands		Sep. 30, 2015		Dec. 31, 2014
Offsetting Assets and Liabilities [Line Items]
Financial derivatives–assets, at fair value	[1]	$ 1,527		$ 3,072
Reverse repurchase agreements	[1]	76,610		13,987
Financial derivatives–liabilities, at fair value	[1]	(16,414)		(8,700)
Repurchase agreements	[1]	(1,225,905)		(1,323,080)
Derivative Liability, Fair Value, Amount Offset Against Collateral		(1,379)		(2,722)
Securities sold under agreements to repurchase available for offset		(76,610)		(13,987)
Derivative Asset, Fair Value, Amount Offset Against Collateral		1,379		2,722
Securities purchased under agreements to resell available for offset		76,610		13,987
Securities Collateral Relating To Repurchase Agreements		1,280,000		1,390,000
Derivative Financial Instruments, Assets [Member]
Offsetting Assets and Liabilities [Line Items]
Financial Instruments Pledged as Collateral	[3]	0	[2]	0	[4]
Cash collateral received	[3]	0	[2]	0	[4]
Derivatives and related collateral, net		148		350
Excess cash collateral				500
Reverse Repurchase Agreements [Member]
Offsetting Assets and Liabilities [Line Items]
Financial Instruments Pledged as Collateral	[3]	0	[2]	0	[4]
Cash collateral received	[3]	0	[2]	0	[4]
Reverse Repurchase Agreements and Related Collateral Net		0		0
Derivative Financial Instruments, Liabilities [Member]
Offsetting Assets and Liabilities [Line Items]
Financial Instruments Pledged as Collateral	[3]	0	[2]	0	[4]
Cash Collateral Pledged	[3]	14,702	[2]	5,783	[4]
Derivatives and related collateral, net		(333)		(195)
Excess cash collateral		8,600		6,300
Repurchase Agreements [Member]
Offsetting Assets and Liabilities [Line Items]
Financial Instruments Pledged as Collateral	[3]	1,134,134	[2]	1,303,360	[4]
Cash Collateral Pledged	[3]	15,161	[2]	5,733	[4]
Repurchase agreements and related collateral, net		$ 0		$ 0

[1] In the Company's Consolidated Balance Sheet, all balances associated with the repurchase agreements and financial derivatives are presented on a gross basis.

[2] For the purpose of this presentation, for each row the total amount of financial instruments transferred or pledged and cash collateral (received) or pledged may not exceed the applicable gross amount of assets or (liabilities) as presented here. Therefore, the Company has reduced the amount of financial instruments transferred or pledged as collateral related to the Company's repurchase agreements and cash collateral pledged on the Company's financial derivative assets and liabilities. Total financial instruments transferred or pledged as collateral on the Company's repurchase agreements as of September 30, 2015 were $1.28 billion. As of September 30, 2015 total cash collateral on financial derivative liabilities excludes $8.6 million of net excess cash collateral.

[3] When collateral is pledged to or pledged by a counterparty, it is often pledged or posted with respect to all positions with such counterparty, and in such cases such collateral cannot be specifically identified as relating to a specific asset or liability. As a result, in preparing the above table, the Company has made assumptions in allocating pledged or posted collateral among the various rows.

[4] For the purpose of this presentation, for each row the total amount of financial instruments transferred or pledged and cash collateral (received) or pledged may not exceed the applicable gross amount of assets or (liabilities) as presented here. Therefore the Company has reduced the amount of financial instruments transferred or pledged as collateral related to the Company's repurchase agreements and cash collateral pledged on the Company's financial derivative assets and liabilities. Total financial instruments transferred or pledged as collateral on the Company's repurchase agreements as of December 31, 2014 were $1.39 billion. As of December 31, 2014 total cash collateral on financial derivative assets and liabilities excludes $0.5 million and $6.3 million, respectively of net excess cash collateral.