Investment Securities Held-to-Maturity - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2021 USD ($) Security	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Security
Schedule of Held-to-maturity Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 2,298,053,000		$ 1,866,989,000
Securities held to maturity at floating rate or adjustable rate	67,000
Commercial Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Sales of held-to-maturity securities	$ 0	$ 0
Held-to-Maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life of investment securities held-to-maturity	4 years 9 months 18 days
Number of securities, temporarily impaired for less than 12 months | Security	149		53
Number of securities, temporarily impaired for 12 months or longer | Security	31		0
Number of securities, temporarily impaired, total | Security	651		600
Held-to-Maturity Securities [Member] | U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life	$ 208,740,000
Federal Home Loan Bank [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities pledged for borrowing at the Federal Home Loan Bank	$ 691,058,000		$ 537,367,000