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Impairment of Investment Securities - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2016 USD ($) Security Bank | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 790,082,000 | $ 891,111,000 |
Estimated Fair Value of Available for Sale | $ 778,612,000 | 886,560,000 |
Number of banks and other financial institutions comprising the security | Bank | 259 |  |
Number Of Pooled Securities with No Senior Class | Security | 2 |  |
Number of Securities with No Excess Subordination | Security | 2 |  |
Number of Securities with Excess Subordination | Security | 6 |  |
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 | $ 6,671,000 | 218,000 | $ 0
Other investments | $ 36,498,000 | 62,952,000 |
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 | 2.00% |  |
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 | 19.00% |  |
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 | 80.00% |  |
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 | 119.00% |  |
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Total unrealized losses | 32.00% |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 39,989,000 | 42,239,000 |
Estimated Fair Value of Available for Sale | 33,292,000 | 35,658,000 |
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 | 62.00% |  |
Corporate Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 5,903,000 | 1,897,000 |
Estimated Fair Value of Available for Sale | $ 6,319,000 | 2,319,000 |
Debt Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Number of securities in an unrealized loss positions | Security | 122 |  |
Estimated Fair Value of Available for Sale | $ 776,942,000 | 884,390,000 |
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 | $ 1,670,000 | 2,170,000 |
Estimated Fair Value of Available for Sale | 1,670,000 | 2,170,000 |
Corporate Securities [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Estimated Fair Value of Available for Sale | $ 6,319,000 | $ 2,319,000 |
Trust Preferred Collateralized Debt Obligations [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Percentage of Current Performing Collateral | 0.00% |  |
Mezzanine [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 39,989,000 |  |
Estimated Fair Value of Available for Sale | 33,292,000 |  |
Mezzanine [Member] | Pre TSL VII [Member] |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | 3,100,000 |  |
Net securities gains (losses) | $ 600,000 |  |

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