Fair Value Measurement and Fair Value of Financial Instruments- Carrying Values and Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial Assets:
Investment securities held to maturity, Carrying Value	$ 84,994	$ 90,766
Investment securities held to maturity, fair value	87,215	93,868
Federal Home Loan Bank and other membership bank stocks, Carrying Value	10,772	11,979
Federal Home Loan Bank and other membership bank stocks, Fair Value	10,772	11,979
Net loans	6,041,694	5,950,108
Fair Value	6,128,887	5,939,413
Financial Liabilities:
Certificates of deposit, Carrying Value	953,370	1,078,256
Certificates of deposit, Fair Value	950,053	1,077,620
Other borrowings, Carrying Value	25,000	25,000
Other borrowings, Fair Value	24,906	25,206
Subordinated debt, Carrying Value	118,267	118,257
Subordinated debentures, Fair Value	117,842	118,208
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Investment securities held to maturity, fair value	0	0
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Other borrowings, Fair Value	0	0
Subordinated debentures, Fair Value	0	0
Significant Other Observable Inputs (Level 2)
Financial Assets:
Investment securities held to maturity, fair value	86,796	93,868
Federal Home Loan Bank and other membership bank stocks, Fair Value	10,772	11,979
Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	950,053	1,077,620
Other borrowings, Fair Value	24,906	25,206
Subordinated debentures, Fair Value	0	0
Significant Unobservable Inputs (Level 3)
Financial Assets:
Investment securities held to maturity, fair value	419	0
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Fair Value	6,128,887	5,939,413
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Other borrowings, Fair Value	0	0
Subordinated debentures, Fair Value	$ 117,842	$ 118,208

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Other Borrowings Fair Value Disclosure

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Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

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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).

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

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The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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Amount of time deposit liabilities, including certificates of deposit.

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