Available-for-sale Securities Classified by Rate Type (Details) - USD ($) $ in Thousands |
Mar. 31, 2017 |
Dec. 31, 2016 |
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| Schedule of Available-for-sale Securities [Line Items] | ||
| Available-for-sale Securities, Adjustable Rate | $ 1,927,115 | $ 1,605,313 |
| Available-for-sale Securities, Fixed Rate | 15,391,582 | 11,523,544 |
| Available-for-sale Securities | 17,318,697 | 13,128,857 |
| Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Available-for-sale Securities, Adjustable Rate | 28,422 | 30,463 |
| Available-for-sale Securities, Fixed Rate | 15,091,463 | 11,196,011 |
| Available-for-sale Securities | 15,119,885 | 11,226,474 |
| Mortgage-backed Securities, Issued by Private Enterprises [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Available-for-sale Securities, Adjustable Rate | 1,898,693 | 1,574,850 |
| Available-for-sale Securities, Fixed Rate | 300,119 | 327,533 |
| Available-for-sale Securities | $ 2,198,812 | $ 1,902,383 |
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- Definition This item represents investments in debt and equity securities with adjustable coupon rates which are categorized neither as held-to-maturity nor trading. No definition available.
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- Definition This item represents investments in debt and equity securities with fixed coupon rates which are categorized neither as held-to-maturity nor trading. No definition available.
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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