Derivatives - Summary Information Regarding Derivatives (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
3rd Party interest rate swaps
Classified in Other Assets:
Notional Amount	$ 293,760	$ 73,075
Average Maturity (Years)	8 years 9 months 18 days	9 years 6 months
Weighted Average Fixed Rate	3.11%	3.20%
Weighted Average Variable Rate	226.00%	255.00%
Fair Value	$ 8,814	$ 503
Classified in Other Liabilities:
Notional Amount	$ 688,585	$ 907,069
Average Maturity (Years)	7 years 10 months 24 days	8 years 8 months 12 days
Weighted Average Fixed Rate	3.93%	3.79%
Weighted Average Variable Rate	193.00%	199.00%
Fair  Value	$ (41,200)	$ (80,231)
Customer interest rate swaps
Classified in Other Assets:
Notional Amount	$ 688,585	$ 907,069
Average Maturity (Years)	7 years 10 months 24 days	8 years 8 months 12 days
Weighted Average Fixed Rate	3.93%	3.79%
Weighted Average Variable Rate	193.00%	199.00%
Fair Value	$ 41,200	$ 80,231
Classified in Other Liabilities:
Notional Amount	$ 293,760	$ 73,075
Average Maturity (Years)	8 years 9 months 18 days	9 years 6 months
Weighted Average Fixed Rate	3.11%	3.20%
Weighted Average Variable Rate	226.00%	255.00%
Fair  Value	$ (8,814)	$ (503)
Interest rate swap (cash flow hedge)
Classified in Other Liabilities:
Notional Amount		$ 30,000
Average Maturity (Years)		6 months
Weighted Average Fixed Rate		1.10%
Fair  Value		$ (143)