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Investment Securities - Additional Information (Detail) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 USD ($) Security | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items] |  |  |
Number of securities in an unrealized loss positions | Security | 2 |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 805,515 | $ 896,495 |
Securities available for sale | 831,223 | 902,292 |
Other than-temporary impairment charge |  | 0 | $ 9,164
Other investments | 10,600 | 15,100 |
Equity Securities, FV-NI | 1,700 |  |
Gross Unrealized Gains (Losses) | 0 | 3,109 |
Amortized Cost | 805,515 | 896,495 |
Held-to-maturity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment | 228,100 | 306,800 |
Available-for-sale Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment | $ 792,100 | 584,800 |
Obligations of U.S. Government-Sponsored Enterprises [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Total unrealized losses | 100.00% |  |
Corporate Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Corporate/Mortgage-Backed Securities, Amortized cost | $ 22,941 | 22,919 |
Securities available for sale | 24,385 | 23,962 |
Gross Unrealized Gains (Losses) | 0 | 0 |
Amortized Cost | 22,941 | 22,919 |
Sales [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Available-for-sale Securities, Gross Realized Losses | 0 | 0 | 4,719
Available-for-sale Securities, Gross Realized Losses | 0 | 7 | 0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments | 0 | (7) | 4,719
Calls And Maturities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Gains | 70 | 29 | 3,383
Available-for-sale Securities, Gross Realized Losses | 0 | 0 | 0
Gain Losses Maturities And Impairment | $ 70 | $ 29 | $ 3,383

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