Offsetting of Assets and Liabilities (Details) - USD ($) $ in Thousands |
Sep. 30, 2017 |
Dec. 31, 2016 |
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| Offsetting of Assets and Liabilities [Line Items] | |||||||||||||||||||
| Financial derivatives–assets, at fair value- | [1] | $ 29,896 | $ 35,595 | ||||||||||||||||
| Fair value repurchase agreements | [1] | 193,070 | 184,819 | ||||||||||||||||
| Derivative Liabilities | [1] | (32,278) | (18,687) | ||||||||||||||||
| Reverse repurchase agreements | [1] | (1,029,810) | (1,033,581) | ||||||||||||||||
| Derivative Liability, Not Offset, Policy Election Deduction | (19,093) | (15,082) | |||||||||||||||||
| Securities Sold under Agreements to Repurchase, Not Offset, Policy Election Deduction | (193,070) | (184,819) | |||||||||||||||||
| Derivative Asset, Not Offset, Policy Election Deduction | 19,093 | 15,082 | |||||||||||||||||
| Securities Purchased under Agreements to Resell, Not Offset, Policy Election Deduction | 193,070 | 184,819 | |||||||||||||||||
| Derivative, Collateral, Obligation to Return Cash | [2],[3] | (3,600) | (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] | 13,112 | 3,574 | ||||||||||||||||
| Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash | [2],[3] | 23,282 | 39,189 | ||||||||||||||||
| Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election | 7,203 | 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 | (73) | (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 | 1,160,000 | 1,160,000 | |||||||||||||||||
| Financial Derivatives - Assets [Member] | |||||||||||||||||||
| Offsetting of Assets and Liabilities [Line Items] | |||||||||||||||||||
| Financial derivatives–assets, at fair value- | 29,896 | [4] | 35,595 | [5] | |||||||||||||||
| Financial Instruments, Owned and Pledged as Collateral, at Fair Value | [2],[3] | 0 | 0 | ||||||||||||||||
| Excess cash collateral | 10,300 | 14,900 | |||||||||||||||||
| Repurchase Agreements [Member] | |||||||||||||||||||
| Offsetting of Assets and Liabilities [Line Items] | |||||||||||||||||||
| Fair value repurchase agreements | 193,070 | [4],[6] | 184,819 | [5],[7] | |||||||||||||||
| 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 | (32,278) | [4] | (18,687) | [5] | |||||||||||||||
| Financial Instruments, Owned and Pledged as Collateral, at Fair Value | [2],[3] | 0 | 0 | ||||||||||||||||
| Excess cash collateral | 18,900 | 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] | $ 813,458 | $ 809,573 | ||||||||||||||||
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