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				100,794				100,794
Other comprehensive loss, net of tax					(110,477)			(110,477)
Dividends declared:
Common				(45,235)				(45,235)
Common stock activity under employee stock plans		309	8,360					8,669
Common stock activity under employee stock plans (in shares)	309,268
Stock-based compensation			3,242					3,242
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						(128)	128	0
Treasury stock issued to benefit plans, net (in shares)	(1,789)
Balance at Jun. 30, 2021		54,064	1,037,088	1,015,742	(48,400)	(5,632)	8,238	2,061,100
Balance (in shares) at Jun. 30, 2021	53,918,695
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				47,944				47,944
Other comprehensive loss, net of tax					61,557			61,557
Dividends declared:
Common				(22,706)				(22,706)
Common stock activity under employee stock plans		45	1,295					1,340
Common stock activity under employee stock plans (in shares)	44,493
Stock-based compensation			1,568					1,568
Treasury stock issued to benefit plans, net						(60)	60	0
Treasury stock issued to benefit plans, net (in shares)	(777)
Balance at Jun. 30, 2021		54,064	1,037,088	1,015,742	(48,400)	(5,632)	8,238	2,061,100
Balance (in shares) at Jun. 30, 2021	53,918,695
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				86,860				86,860
Other comprehensive loss, net of tax					(468,100)			(468,100)
Dividends declared:
Common				(46,482)				(46,482)
Common stock activity under employee stock plans		93	706					799
Common stock activity under employee stock plans (in shares)	92,695
Stock-based compensation			4,190					4,190
Distribution of stock under deferred compensation arrangements			103			739	(842)	0
Distribution of stock under deferred compensation arrangements (in shares)	14,934
Treasury stock purchased						(16,378)		(16,378)
Treasury stock purchased (in shares)	(250,000)
Treasury stock issued to benefit plans, net						(120)	120	0
Treasury stock issued to benefit plans, net (in shares)	(1,649)
Balance at Jun. 30, 2022		54,185	1,046,303	1,098,664	(518,727)	(26,369)	7,640	1,661,696
Balance (in shares) at Jun. 30, 2022	53,734,027
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				39,805				39,805
Other comprehensive loss, net of tax					(196,733)			(196,733)
Dividends declared:
Common				(23,248)				(23,248)
Common stock activity under employee stock plans		21	293					314
Common stock activity under employee stock plans (in shares)	21,481
Stock-based compensation			2,304					2,304
Distribution of stock under deferred compensation arrangements			(1)			1		0
Distribution of stock under deferred compensation arrangements (in shares)	20
Treasury stock purchased						(12,849)		(12,849)
Treasury stock purchased (in shares)	(200,000)
Treasury stock issued to benefit plans, net						(57)	57	0
Treasury stock issued to benefit plans, net (in shares)	(836)
Balance at Jun. 30, 2022		$ 54,185	$ 1,046,303	$ 1,098,664	$ (518,727)	$ (26,369)	$ 7,640	$ 1,661,696
Balance (in shares) at Jun. 30, 2022	53,734,027