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Securities - Additional Information (Detail) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 USD ($) Investment | Sep. 30, 2019 USD ($) Investment | Dec. 31, 2018 USD ($) Investment
Schedule of Investments [Line Items] |  |  |  |
Federal Home Loan Bank stock, at cost | $ | [1] | $ 606,371 | $ 606,371 | $ 644,590
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses | $ |  | $ 8,400 | $ 8,400 | $ 22,500
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost |  | 2.80% | 2.80% | 2.90%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost | $ |  | $ 299,400 | $ 299,400 | $ 782,400
Net unrealised gains losses on equity securities recognised | $ |  | $ 275,000 | $ 2,300 |
Mortgage-related Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 3 | 3 | 9
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 | 5
Municipal bonds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 1 | 1 | 3
Mutual Fund |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 1 | 1 | 1
US Government agencies securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 6 | 6 | 9
Collateralized mortgage obligations |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more |  | 2 | 2 | 7
[1] | Carrying value and estimated fair value are at cost.

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- Definition Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Amortized Cost. + References No definition available. + Details
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- Definition Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Percentage Below Amortized Cost. + References No definition available. + Details
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- Definition Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714 + Details
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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 325 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809 + Details
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