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Impairment of Investment Securities - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2015 USD ($) Security Bank | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 891,111,000 | $ 1,317,318,000 |
Estimated Fair Value of Available for Sale | $ 886,560,000 | 1,309,819,000 |
Number of banks and other financial institutions comprising the security | Bank | 275 |  |
Number Of Pooled Securities with No Senior Class | Security | 3 |  |
Number of Securities with No Excess Subordination | Security | 4 |  |
Number of Securities with Excess Subordination | Security | 5 |  |
Collateral issued by financial institutions | $ 15,000,000,000 |  |
Coupon interest rate | 7.00% |  |
Prepayment rate | 5.00% |  |
Estimate of future cash flows prepayment percentage in year three | 40.00% |  |
Estimate of future cash flows prepayment percentage thereafter | 2.00% |  |
Fair Value Input Coupon Rates | 10.00% |  |
Probability of default | 100.00% |  |
Projected recovery rate | 0.00% |  |
Probability percentage assigned to default bank subject to market indicators | 10.00% |  |
Probability percentage assigned to default bank | 100.00% |  |
Other than-temporary impairment charge | $ 218,000 | 0 | $ 13,356,000
Net securities (losses) gains | (153,000) | 550,000 | (1,158,000)
Other investments | $ 62,952,000 | 44,545,000 |
Minimum [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Subordinated tranches range | 7.00% |  |
Total principal amount of the respective securities | 5.00% |  |
Excess subordination as a percentage of current performing collateral | 10.00% |  |
Collateral issued by financial institutions | $ 15,000,000,000 |  |
Probabilities for performing collateral range | 0.33% |  |
Excess percent value of future cash flows over current book value | 20.00% |  |
Over Fifteen Million [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Prepayment rate | 100.00% |  |
Maximum [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Subordinated tranches range | 35.00% |  |
Excess subordination as a percentage of current performing collateral | 84.00% |  |
Collateral issued by financial institutions | $ 2,000,000,000 |  |
Probabilities for performing collateral range | 75.00% |  |
Excess percent value of future cash flows over current book value | 133.00% |  |
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Total unrealized losses | 40.00% |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 42,239,000 | 41,926,000 |
Estimated Fair Value of Available for Sale | 35,658,000 | 28,999,000 |
Other than-temporary impairment charge | $ 0 | 0 | $ 0
Obligations of U.S. Government-Sponsored Enterprises [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Total unrealized losses | 59.00% |  |
Corporate Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 1,897,000 | 6,682,000 |
Estimated Fair Value of Available for Sale | $ 2,319,000 | 7,255,000 |
US States and Political Subdivisions Debt Securities [Member] | Other Government - Sponsored Enterprises [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Total unrealized losses | 1.00% |  |
Debt Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Number of securities in an unrealized loss positions | Security | 80 |  |
Equity Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Number of securities in an unrealized loss positions | Security | 0 |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 2,170,000 | 1,420,000 |
Estimated Fair Value of Available for Sale | 2,170,000 | $ 1,420,000 |
Mm Comm Ix [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Other than-temporary impairment charge | 13,400,000 |  |
Corporate Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | 6,600,000 |  |
Net securities (losses) gains | $ 1,300,000 |  |
Trust preferred collateralized debt obligations [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Percentage of Current Performing Collateral | 0.00% |  |

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