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Capital and Regulatory Matters (Narrative) (Detail) |  |  |  |  | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 24, 2017 USD ($) shares | Mar. 17, 2017 USD ($) | Jan. 01, 2016 | Feb. 15, 2013 USD ($) $ / shares shares | Feb. 28, 2007 USD ($) | Dec. 31, 2017 USD ($) quarter $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) shares | Jan. 01, 2019 | Oct. 27, 2016 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Non-cumulative perpetual preferred stock |  |  |  |  |  | $ 144,500,000 | $ 144,500,000 |  |  |
Non-cumulative perpetual preferred stock, dividend rate percentage |  |  |  |  |  | 5.375% | 5.375% |  |  |
Additional Tier 1 Capital beyond Common Equity Tier 1 |  |  |  |  |  | $ 0 | $ 0 |  |  |
Subordinated notes |  |  |  |  |  | $ 98,552,000 | $ 99,990,000 |  |  |
Preferred stock, shares issued | shares |  |  |  |  |  | 6,000,000 | 6,000,000 |  |  |
Preferred stock, par value | $ / shares |  |  |  |  |  | $ 0.01 | $ 0.01 |  |  |
Proceeds from issuance of preferred stock |  |  |  | $ 144,500,000 |  |  |  |  |  |
Share repurchase authorized amount | $ 150,000,000 |  |  |  |  |  |  | $ 100,000,000 |  | $ 100,000,000
Stock repurchase program, period in force | 2 years |  |  |  |  |  |  |  |  |
Treasury stock, shares, acquired | shares |  |  |  |  |  | 1,149,555 | 17,233 | 1,504,146 |  |
Aggregate dividends available for payment without prior regulatory approval |  |  |  |  |  | $ 544,800,000 |  |  |  |
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter |  |  |  |  |  | 20 |  |  |  |
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio |  |  |  |  |  |  |  |  | 4.50% |
Capital Conservation Buffer |  |  |  |  |  |  |  |  | 2.50% |
Minimum ratio of Tier 1 capital to risk-weighted assets |  |  |  |  |  |  |  |  | 6.00% |
Minimum ratio of Total capital to risk weighted assets |  |  |  |  |  |  |  |  | 8.00% |
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation |  |  |  |  |  |  |  |  | 7.00% |
Effective tier one capital ratio, upon full implementation |  |  |  |  |  |  |  |  | 8.50% |
Tier one risk based capital to risk weighted assets, ratio upon full implementation |  |  |  |  |  |  |  |  | 10.50% |
Minimum leverage ratio |  |  |  |  |  |  |  |  | 4.00% |
Two Thousand And Sixteen [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Tier one capital conservation buffer to risk weighted assets required under regulatory |  |  | 0.625% |  |  |  |  |  |  |
Tier one risk based capital conservation buffer initial requirements phasing duration |  |  | 4 years |  |  |  |  |  |  |
Series A Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Non-cumulative perpetual preferred stock, dividend rate percentage |  |  |  | 5.375% |  |  |  |  |  |
Preferred stock, shares issued | shares |  |  |  | 6,000,000 |  |  |  |  |  |
Series A Preferred Stock, Liquidation preference value |  |  |  | $ 150,000,000 |  | $ 25 | $ 25 |  |  |
Preferred stock, par value | $ / shares |  |  |  | $ 0.01 |  |  |  |  |  |
Liquidation preference per share | $ / shares |  |  |  | $ 25 |  |  |  |  |  |
Treasury Stock [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Treasury stock, shares, acquired | shares | 0 |  |  |  |  | 1,134,966 |  | 1,485,493 |  |
Trust Preferred Securities Tier Two Capital Allowable Portion [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Trust preferred securities |  |  |  |  |  | $ 133,000,000 | 133,000,000 |  |  |
Subordinated Debt [Member] |  |  |  |  |  |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |  |  |  |  |  |
Permissible portion of subordinated note included in total capital |  |  |  |  |  | $ 100,000,000 | $ 0 |  |  |
Subordinated notes interest rate |  | 4.50% |  |  | 5.75% |  |  |  |  |
Per year percentage of decreases in permissible portion of Subordinate Note included in Total Capital |  |  |  |  |  | 20.00% |  |  |  |
Final years of the term of the notes |  |  |  |  |  | 5 years |  |  |  |
Subordinated notes |  | $ 100,000,000 |  |  | $ 100,000,000 |  |  |  |  |

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