Offsetting of Assets and Liabilities (Details) - USD ($) $ in Thousands		Jun. 30, 2017		Dec. 31, 2016
Offsetting of Assets and Liabilities [Line Items]
Financial derivatives–assets, at fair value-	[1]	$ 26,602		$ 35,595
Securities Purchased under Agreements to Resell	[1]	266,659		184,819
Derivative Liabilities	[1]	(27,003)		(18,687)
Reverse repurchase agreements	[1]	(1,119,238)		(1,033,581)
Derivative Liability, Not Offset, Policy Election Deduction		(16,748)		(15,082)
Securities Sold under Agreements to Repurchase, Not Offset, Policy Election Deduction		(266,659)		(184,819)
Derivative Asset, Not Offset, Policy Election Deduction		16,748		15,082
Securities Purchased under Agreements to Resell, Not Offset, Policy Election Deduction		266,659		184,819
Derivative, Collateral, Obligation to Return Cash	[2],[3]	(3,898)		(7,933)
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Cash	[2],[3]	0		0
Derivative, Collateral, Right to Reclaim Cash	[2],[3]	10,255		3,574
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	[2],[3]	17,501		39,189
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election		5,956		12,580
Securities Purchased under Agreements to Resell, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election		0		0
Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election		0		(31)
Securities Sold under Agreements to Repurchase, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election		0		0
Securities Collateral relating to Reverse Repurchase Agreements		1,270,000		1,160,000
Financial Derivatives - Assets [Member]
Offsetting of Assets and Liabilities [Line Items]
Financial derivatives–assets, at fair value-		26,602	[4]	35,595	[5]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	[2],[3]	0		0
Excess cash collateral		7,200		14,900
Repurchase Agreements [Member]
Offsetting of Assets and Liabilities [Line Items]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	[2],[3]	0		0
Financial Derivatives - Liabilities [Member]
Offsetting of Assets and Liabilities [Line Items]
Derivative Liabilities		(27,003)	[4]	(18,687)	[5]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	[2],[3]	0		0
Excess cash collateral		17,200		14,800
Reverse Repurchase Agreements [Member]
Offsetting of Assets and Liabilities [Line Items]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	[2],[3]	$ 835,078		$ 809,573

[1] In the Company's Consolidated Statement of Assets, Liabilities, and Equity, all balances associated with repurchase agreements, reverse 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 reverse repurchase agreements and cash collateral pledged on the Company's financial derivative liabilities. Total financial instruments transferred or pledged as collateral on the Company's reverse repurchase agreements as of June 30, 2017 and December 31, 2016 were $1.27 billion and $1.16 billion, respectively. As of June 30, 2017 and December 31, 2016, total cash collateral on financial derivative assets excludes excess net cash collateral pledged of $7.2 million and $14.9 million, respectively. As of June 30, 2017 and December 31, 2016, total cash collateral on financial derivative liabilities excludes excess cash collateral pledged of $17.2 million and $14.8 million, respectively.

[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 tables, the Company has made assumptions in allocating pledged or posted collateral among the various rows.

[4] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.

[5] See Note 2 and Note 3 in Notes to Consolidated Financial Statements.