Securities Available-for-Sale - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019 USD ($) Security	Dec. 31, 2018 USD ($) Security	Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 1,776,399,000	$ 1,441,059,000
Securities available-for-sale are securities at fair value pledged for borrowing	32,297,000	34,787,000
Gross gains on sales of securities	61,000	302,000	$ 47,000
Proceeds from sales of securities available-for-sale	16,285,000	27,517,000	18,180,000
Securities at floating rate or adjustable rate	244,688,000
Federal Home Loan Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross gains on sales of securities	$ 13,000	$ 302,000	$ 47,000
Securities AFS [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average remaining life of investment securities available-for-sale	5 years 4 months 24 days
Number of securities, temporarily impaired for less than 12 months | Security	45	10
Number of securities, temporarily impaired for 12 months or longer | Security	18	30
Number of securities, temporarily impaired, total | Security	122	190
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 186,245,000	$ 197,304,000