CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock Shares Outstanding [Member]	Common Stock Amount Issued [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss)/Income [Member]	Treasury Stock [Member]	Deferred Compensation Arrangements [Member]	Total
Balance at Dec. 31, 2020		$ 53,755	$ 1,025,163	$ 960,183	$ 62,077	$ (6,198)	$ 9,127	$ 2,104,107
Balance (in shares) at Dec. 31, 2020	53,593,127
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				52,850				52,850
Other comprehensive loss, net of tax					(172,034)			(172,034)
Cash dividends declared:
Common				(22,529)				(22,529)
Common stock activity under employee stock ownership plans		264	7,065					7,329
Common stock activity under employee stock ownership plans (in shares)	264,775
Stock-based compensation			1,674					1,674
Distribution of stock under deferred compensation arrangements			323			694	(1,017)	0
Distribution of stock under deferred compensation arrangements (in shares)	18,089
Treasury stock issued to benefit plans, net						(68)	68	0
Treasury stock issued to benefit plans, net (in shares)	(1,012)
Balance at Mar. 31, 2021		54,019	1,034,225	990,504	(109,957)	(5,572)	8,178	1,971,397
Balance (in shares) at Mar. 31, 2021	53,874,979
Balance at Dec. 31, 2021		54,092	1,041,304	1,058,286	(50,627)	(10,610)	8,362	2,100,807
Balance (in shares) at Dec. 31, 2021	53,878,047
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				47,055				47,055
Other comprehensive loss, net of tax					(271,367)			(271,367)
Cash dividends declared:
Common				(23,234)				(23,234)
Common stock activity under employee stock ownership plans		72	413					485
Common stock activity under employee stock ownership plans (in shares)	71,214
Stock-based compensation			1,886					1,886
Distribution of stock under deferred compensation arrangements			104			738	(842)	0
Distribution of stock under deferred compensation arrangements (in shares)	14,914
Treasury stock issued to benefit plans, net						(63)	63	0
Treasury stock issued to benefit plans, net (in shares)	(813)
Treasury stock purchased						(3,529)		(3,529)
Treasury stock purchased (in shares)	(50,000)
Balance at Mar. 31, 2022		$ 54,164	$ 1,043,707	$ 1,082,107	$ (321,994)	$ (13,464)	$ 7,583	$ 1,852,103
Balance (in shares) at Mar. 31, 2022	53,913,362