Estimated Fair Value of Financial Instruments and Fair Value Measurement- Carrying Values and Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial Assets:
Investment securities held to maturity, Carrying Value	$ 158,576	$ 139,685
Investment securities held to maturity, Fair Value	153,975	138,688
Federal Home Loan Bank and other membership bank stocks, Carrying Value	13,458	12,576
Federal Home Loan Bank and other membership bank stocks, Fair Value	13,458	12,576
Loans and leases, net Carrying Value	4,290,825	4,117,265
Loans and leases, net Fair Value	4,264,827	4,114,516
Financial Liabilities:
Certificates of deposit, Carrying value	790,829	737,428
Certificates of deposit, Fair Value	782,618	732,417
Other borrowings, Carrying value	184,640	192,011
Other borrowings, Fair Value	180,875	189,080
Subordinated debentures, Carrying Value	104,995	104,902
Subordinated debentures, Fair Value	103,146	97,244
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
Loans and leases, net 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	147,576	127,901
Federal Home Loan Bank and other membership bank stocks, Fair Value	13,458	12,576
Loans and leases, net Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	782,618	732,417
Other borrowings, Fair Value	180,875	189,080
Subordinated debentures, Fair Value	0	0
Significant Unobservable Inputs (Level 3)
Financial Assets:
Investment securities held to maturity, Fair Value	6,399	10,787
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Loans and leases, net Fair Value	4,264,827	4,114,516
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Other borrowings, Fair Value	0	0
Subordinated debentures, Fair Value	$ 103,146	$ 97,244

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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 after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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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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