Derivative Instruments and Hedging Activities U.S. Treasury Futures (Details) - USD ($) |
Sep. 30, 2019 |
Jun. 30, 2019 |
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Dec. 31, 2017 |
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| Derivative [Line Items] | ||||||
| Notional | $ 54,226,205,000 | $ 55,549,424,000 | $ 36,528,169,000 | $ 41,330,283,000 | $ 28,618,861,000 | $ 31,226,878,000 |
| Derivative Financial Instruments, Liabilities [Member] | ||||||
| Derivative [Line Items] | ||||||
| Notional | 43,731,262,000 | 5,403,265,000 | ||||
| Fair Value | (17,201,000) | $ (820,590,000) | ||||
| U.S. Treasury Futures [Member] | ||||||
| Derivative [Line Items] | ||||||
| Notional | 300,000,000 | |||||
| U.S. Treasury Futures [Member] | Derivative Financial Instruments, Liabilities [Member] | ||||||
| Derivative [Line Items] | ||||||
| Notional | 320,000,000 | |||||
| Fair Value | $ (1,471,000) |
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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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- Definition Nominal or face amount used to calculate payment on derivative. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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