Fair Value Measurement and Fair Value of Financial Instruments- Carrying Values and Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Assets:
Investment securities held to maturity, Carrying Value	$ 97,893	$ 123,975
Investment securities held to maturity, fair value	101,205	124,904
Federal Home Loan Bank and other membership bank stocks, Carrying Value	14,235	22,505
Federal Home Loan Bank and other membership bank stocks, Fair Value	14,235	22,505
Net loans	5,778,349	5,097,820
Fair Value	5,784,132	5,194,065
Financial Liabilities:
Certificates of deposit, Carrying Value	1,144,341	870,804
Certificates of deposit, Fair Value	1,144,945	871,418
Other borrowings, Carrying Value	135,111	165,816
Other borrowings, Fair Value	138,863	166,505
Subordinated debt, Carrying Value	118,248	118,220
Subordinated debentures, Fair Value	116,697	117,992
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	98,705	121,503
Federal Home Loan Bank and other membership bank stocks, Fair Value	14,235	22,505
Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	1,144,945	871,418
Other borrowings, Fair Value	138,863	166,505
Subordinated debentures, Fair Value	0	0
Significant Unobservable Inputs (Level 3)
Financial Assets:
Investment securities held to maturity, fair value	2,500	3,401
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Fair Value	5,784,132	5,194,065
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Other borrowings, Fair Value	0	0
Subordinated debentures, Fair Value	$ 116,697	$ 117,992

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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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Amount of time deposit liabilities, including certificates of deposit.

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