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Securities - Additional Information (Detail) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2015 USD ($) Investment | Dec. 31, 2014 USD ($) Investment | Dec. 31, 2013 USD ($)
Schedule of Investments [Line Items] |  |  |  |
Federal Home Loan Bank stock, at cost | $ | [1] | $ 663,971 | $ 515,327 |
Proceeds from sales of held to maturity securities | $ |  | 44,104 | 139,294 | $ 191,142
Gain realized gains from sales of held to maturity securities | $ |  | 2,900 | 7,800 |
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses | $ |  | $ 24,900 | $ 51,600 |
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost |  | 2.00% | 1.90% |
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost | $ |  | $ 1,200,000 | $ 2,700,000 |
Agency Debt Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 7 | 17 |
Capital trust notes |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 5 | 5 |
Mortgage-Related Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 2 | 16 |
GSE CMOs |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  |  | 3 |
Municipal bonds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  |  | 2 |
Preferred stock securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  |  | 1 |
Minimum |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Percentage of amount collected to recognize sale of securities |  | 85.00% | 85.00% |
[1] | Carrying value and estimated fair value are at cost.

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- Definition Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809 + Details
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