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Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaptions (Details) (USD $)
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3 Months Ended | 12 Months Ended |
|---|---|---|
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Mar. 31, 2012
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Dec. 31, 2011
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Options Held [Member]
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| Derivative [Line Items] | ||
| Derivative, Lower Remaining Maturity Range | < 6 Months | |
| Derivative, Higher Remaining Maturity Range | ≥ 6 Months | ≥ 6 Months |
| Derivative, Cost | $ 44,618,000 | $ 29,670,000 |
| Derivative Asset, Fair Value, Net | 30,214,000 | 5,635,000 |
| Derivative, Average Remaining Maturity | 15.8949 | 12.2647 |
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Underlying Swap [Member]
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| Derivative [Line Items] | ||
| Derivative, Average Remaining Maturity | 7.0698 | 4.931 |
| Derivative, Notional Amount | 4,300,000,000 | 2,900,000,000 |
| Derivative, Average Fixed Interest Rate | 3.4506% | 3.2065% |
| Derivative, Description of Variable Rate Basis | 3M Libor | 3M Libor |
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Six Months or Longer Remaining Maturity [Member] | Options Held [Member]
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| Derivative [Line Items] | ||
| Derivative, Cost | 30,965,000 | 13,523,000 |
| Derivative Asset, Fair Value, Net | 29,762,000 | 5,631,000 |
| Derivative, Average Remaining Maturity | 16.4031 | 12.2706 |
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Six Months or Longer Remaining Maturity [Member] | Underlying Swap [Member]
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| Derivative [Line Items] | ||
| Derivative, Average Remaining Maturity | 9.28 | 6.462 |
| Derivative, Notional Amount | 2,500,000,000 | 1,300,000,000 |
| Derivative, Average Fixed Interest Rate | 3.73% | 3.1923% |
| Derivative, Description of Variable Rate Basis | 3M Libor | 3M Libor |
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Less Than Six Months Remaining Maturity [Member] | Options Held [Member]
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| Derivative [Line Items] | ||
| Derivative, Cost | 13,653,000 | 16,147,000 |
| Derivative Asset, Fair Value, Net | 452,000 | 4,000 |
| Derivative, Average Remaining Maturity | 5.8405 | 4.9724 |
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Less Than Six Months Remaining Maturity [Member] | Underlying Swap [Member]
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| Derivative [Line Items] | ||
| Derivative, Average Remaining Maturity | 4 | 3.688 |
| Derivative, Notional Amount | $ 1,800,000,000 | $ 1,600,000,000 |
| Derivative, Average Fixed Interest Rate | 3.0625% | 3.218% |
| Derivative, Description of Variable Rate Basis | 3M Libor | 3M Libor |