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Securities - Additional Information (Detail) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 USD ($) Investment | Mar. 31, 2015 USD ($) | Dec. 31, 2015 USD ($) Investment
Schedule of Investments [Line Items] |  |  |  |
Federal Home Loan Bank stock, at cost | [1] | $ 551,247,000 |  | $ 663,971,000
Gross realized losses |  | 0 | $ 0 |
Investment securities designated as having a continuous loss position for twelve months or more, unrealized losses |  | $ 19,100,000 |  | $ 24,900,000
Investment securities designated as having a continuous loss position for twelve months or more, percentage below collective amortized cost |  | 39.10% |  | 2.00%
Investment securities designated as having a continuous loss position for twelve months or more, amortized cost |  | $ 48,800,000 |  | $ 1,200,000,000
Agency Debt Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment |  |  |  | 7
Capital trust notes |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of investment securities designated as having a continuous loss position for twelve months or more | Investment |  | 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 | Investment |  | 3 |  | 2
[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 This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + 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://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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