Fair Value Measurement - Carrying Amount and Fair Value of Financial Instruments Not Measured at Fair Value on a Recurring or Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Financial Assets:
Cash and due from financial institutions	$ 194,773	$ 48,535	$ 62,219	$ 42,779
Other securities	20,537	20,280
Loans, net of allowance	2,018,303	1,694,203
Bank owned life insurance	45,732	44,999
Accrued interest receivable	10,227	7,093
Financial Liabilities:
Short-term FHLB advances		101,500
Long-term FHLB advances	125,000	125,000
Other borrowings	183,695
Securities sold under agreement to repurchase	25,813	18,674
Carrying Amount [Member]
Financial Assets:
Cash and due from financial institutions	194,773	48,535
Other securities	20,537	20,280
Loans, held for sale	13,256	2,285
Loans, net of allowance	2,018,303	1,694,203
Bank owned life insurance	45,732	44,999
Accrued interest receivable	10,227	7,093
Financial Liabilities:
Nonmaturing deposits	1,776,668	1,402,924
Time deposits	292,101	275,840
Short-term FHLB advances		101,500
Long-term FHLB advances	125,000	125,000
Other borrowings	183,695
Securities sold under agreement to repurchase	25,813	18,674
Subordinated debentures	29,427	29,427
Accrued interest payable	492	277
Total Fair Value [Member]
Financial Assets:
Cash and due from financial institutions	194,773	48,535
Other securities	20,537	20,280
Loans, held for sale	13,521	2,331
Loans, net of allowance	2,046,882	1,713,863
Bank owned life insurance	45,732	44,999
Accrued interest receivable	10,227	7,093
Financial Liabilities:
Nonmaturing deposits	1,776,668	1,402,924
Time deposits	293,168	276,616
Short-term FHLB advances		101,500
Long-term FHLB advances	131,095	123,893
Other borrowings	183,677
Securities sold under agreement to repurchase	25,813	18,674
Subordinated debentures	31,990	34,452
Accrued interest payable	492	277
(Level 1) [Member]
Financial Assets:
Cash and due from financial institutions	194,773	48,535
Other securities	20,537	20,280
Loans, held for sale	13,521	2,331
Bank owned life insurance	45,732	44,999
Accrued interest receivable	10,227	7,093
Financial Liabilities:
Nonmaturing deposits	1,776,668	1,402,924
Short-term FHLB advances		101,500
Securities sold under agreement to repurchase	25,813	18,674
Accrued interest payable	492	277
(Level 3) [Member]
Financial Assets:
Loans, net of allowance	2,046,882	1,713,863
Financial Liabilities:
Time deposits	293,168	276,616
Long-term FHLB advances	131,095	123,893
Other borrowings	183,677
Subordinated debentures	$ 31,990	$ 34,452