Condensed Financial Information - Parent Company Only - Schedule of Condensed Cash Flow Statement (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income		$ 71,104,000	$ 78,120,000	$ 91,801,000
Adjustments to reconcile net income to net cash provided by operating activities:
Bank owned life insurance income	[1]	(3,185,000)	(3,787,000)	(3,981,000)
Depreciation of premises and equipment		5,057,000	4,465,000	4,662,000
Stock-based compensation		4,194,000	4,120,000	3,698,000
Contributions to pension and other postretirement benefit plans		(250,000)	(252,000)	(265,000)
(Increase) decrease in other assets		(8,877,000)	(5,859,000)	(3,131,000)
Increase in accrued interest payable and other liabilities		17,150,000	5,993,000	2,195,000
Net cash provided by operating activities		89,741,000	109,455,000	102,337,000
Cash flows from investing activities:
Net cash used in investing activities		(454,436,000)	(897,612,000)	(126,779,000)
Cash flows from financing activities:
Proceeds from issuance of subordinated notes		0	50,000,000	0
Payment for shares withheld to cover taxes on vesting of restricted stock units		(1,232,000)	(903,000)	(355,000)
Purchases of treasury stock		(462,000)	(11,381,000)	(295,000)
Stock issued under dividend reinvestment and employee stock purchase plans		2,565,000	2,541,000	2,384,000
Proceeds from exercise of stock options		115,000	698,000	2,058,000
Cash dividends paid		(25,050,000)	(24,607,000)	(23,575,000)
Net cash provided by financing activities		461,695,000	50,806,000	694,734,000
Cash and cash equivalents at beginning of year		152,799,000	890,150,000	219,858,000
Cash and cash equivalents at end of year		249,799,000	152,799,000	890,150,000
Cash paid during the year for:
Interest		139,600,000	32,668,000	21,824,000
Income tax, net of refunds received		16,784,000	11,859,000	26,589,000
Parent Company [Member]
Cash flows from operating activities:
Net income		71,104,000	78,120,000	91,801,000
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income of subsidiaries		(61,719,000)	(60,299,000)	(42,211,000)
Bank owned life insurance income		(118,000)	(116,000)	(111,000)
Depreciation of premises and equipment		342,000	346,000	304,000
Stock-based compensation		4,194,000	4,120,000	3,698,000
Contributions to pension and other postretirement benefit plans		(250,000)	(252,000)	(265,000)
(Increase) decrease in other assets		(4,526,000)	7,561,000	(5,654,000)
Increase in accrued interest payable and other liabilities		2,975,000	(4,256,000)	2,510,000
Net cash provided by operating activities		12,002,000	25,224,000	50,072,000
Cash flows from investing activities:
Investments in subsidiaries		0	(10,000,000)	0
Proceeds from sales of securities		0	1,000	0
Other, net		(478,000)	(272,000)	(68,000)
Net cash used in investing activities		(478,000)	(10,271,000)	(68,000)
Cash flows from financing activities:
Proceeds from issuance of subordinated notes		0	49,051,000	0
Repayments of Subordinated Debt		0	0	(85,000,000)
Payment for shares withheld to cover taxes on vesting of restricted stock units		(1,232,000)	(903,000)	(355,000)
Purchases of treasury stock		(462,000)	(11,381,000)	(295,000)
Stock issued under dividend reinvestment and employee stock purchase plans		2,565,000	2,541,000	2,384,000
Proceeds from exercise of stock options		115,000	698,000	2,058,000
Cash dividends paid		(25,050,000)	(24,607,000)	(23,575,000)
Net cash provided by financing activities		(24,064,000)	15,399,000	(104,783,000)
Net increase (decrease) in cash and cash equivalents		(12,540,000)	30,352,000	(54,779,000)
Cash and cash equivalents at beginning of year		130,206,000	99,854,000	154,633,000
Cash and cash equivalents at end of year		117,666,000	130,206,000	99,854,000
Cash paid during the year for:
Interest		8,625,000	5,000,000	6,929,000
Income tax, net of refunds received		$ 15,266,000	$ 10,989,000	$ 18,130,000

[1] Net interest income as well as many other revenues for financial assets and liabilities including loans, leases, securities, and derivatives are excluded from the scope of FASB ASC 606 "Revenue from Contracts with Customers" ("FASB ASC 606"). Noninterest income streams that are out of scope of FASB ASC 606 include bank owned life insurance income, sales of investment securities and mortgage banking activities.