Consolidated Statements of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Shares, Outstanding		73,249
Adjustment to opening retained earnings, net of tax, pursuant to adoption of ASU | Accounting Standards Update 2016-02 [Member]	$ 782		$ 782
Balance, value at Dec. 31, 2018	2,033,649	$ 1,642,246	426,708	$ (35,305)
Net income	148,322		148,322
Other comprehensive income (loss)	100,189			100,189
Issuance of common stock - stock option and other plans, shares		58
Issuance of common stock - stock option and other plans, value	$ 2,025	$ 2,025
Stock Adjustment Deferred Compensation - Shares	0
Stock Adjustment Value Deferred Compensation	$ 2
Issuance of common stock - restricted stock awards, net of canceled awards, shares		354
Issuance of common stock - restricted stock awards, net of canceled awards, value	6,827	$ 6,827
Purchase and retirement of common stock, Shares		(73)
Purchase and retirement of common stock, Value	(2,765)	$ (2,765)
Cash dividends declared on common stock	(82,074)		(82,074)
Purchase of treasury stock, Shares		(1,300)
Purchase of treasury stock, value	(45,380)				$ (45,380)
Balance, value at Sep. 30, 2019	2,161,577	$ 1,648,335	493,738	64,884	(45,380)
Shares, Outstanding		72,924
Balance, value at Jun. 30, 2019	2,133,638	$ 1,644,922	463,429	47,150	(21,863)
Net income	50,727		50,727
Other comprehensive income (loss)	17,734			17,734
Issuance of common stock - stock option and other plans, shares		31
Issuance of common stock - stock option and other plans, value	$ 1,132	$ 1,132
Stock Adjustment Deferred Compensation - Shares	0
Stock Adjustment Value Deferred Compensation	$ 1
Issuance of common stock - restricted stock awards, net of canceled awards, shares		9
Issuance of common stock - restricted stock awards, net of canceled awards, value	2,299	$ 2,299
Purchase and retirement of common stock, Shares		0
Purchase and retirement of common stock, Value	(19)	$ (19)
Cash dividends declared on common stock	(20,418)		(20,418)
Purchase of treasury stock, Shares		(676)
Purchase of treasury stock, value	(23,517)				(23,517)
Balance, value at Sep. 30, 2019	2,161,577	$ 1,648,335	493,738	64,884	(45,380)
Shares, Outstanding		72,288
Shares, Outstanding		72,124
Adjustment to opening retained earnings, net of tax, pursuant to adoption of ASU | Accounting Standards Update 2016-13 [Member]	(2,500)		(2,457)
Balance, value at Dec. 31, 2019	2,159,962	$ 1,650,753	519,676	40,367	(50,834)
Net income	95,944		95,944
Other comprehensive income (loss)	137,234			137,234
Issuance of common stock - stock option and other plans, shares		65
Issuance of common stock - stock option and other plans, value	2,028	$ 2,028
Stock Adjustment Deferred Compensation - Shares		0
Stock Adjustment Value Deferred Compensation	2	$ 2
Issuance of common stock - restricted stock awards, net of canceled awards, shares		222
Issuance of common stock - restricted stock awards, net of canceled awards, value	7,918	$ 7,918
Purchase and retirement of common stock, Shares		(67)
Purchase and retirement of common stock, Value	(2,498)	$ (2,498)
Cash dividends declared on common stock	$ (76,152)		(76,152)
Purchase of treasury stock, Shares	(731)	(731)
Purchase of treasury stock, value	$ (20,000)				(20,000)
Balance, value at Sep. 30, 2020	2,301,981	$ 1,658,203	537,011	177,601	(70,834)
Shares, Outstanding		71,586
Balance, value at Jun. 30, 2020	2,276,755	$ 1,654,129	512,383	181,077	(70,834)
Net income	44,734		44,734
Other comprehensive income (loss)	(3,476)			(3,476)
Issuance of common stock - stock option and other plans, shares		39
Issuance of common stock - stock option and other plans, value	1,083	$ 1,083
Stock Adjustment Deferred Compensation - Shares		0
Stock Adjustment Value Deferred Compensation	(2)	$ (2)
Issuance of common stock - restricted stock awards, net of canceled awards, shares		(12)
Issuance of common stock - restricted stock awards, net of canceled awards, value	3,009	$ 3,009
Purchase and retirement of common stock, Shares		0
Purchase and retirement of common stock, Value	(16)	$ (16)
Cash dividends declared on common stock	(20,106)		(20,106)
Balance, value at Sep. 30, 2020	$ 2,301,981	$ 1,658,203	$ 537,011	$ 177,601	$ (70,834)
Shares, Outstanding		71,613