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			72,124
Adjustment to opening retained earnings, net of tax, pursuant to adoption of ASU | Accounting Standards Update 2016-13 [Member]		$ (2,457)		$ (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 - employee stock purchase plan, shares			65
Issuance of common stock - employee stock purchase plan, value		$ 2,028	$ 2,028
Activity in Deferred Compensation Plan, shares		0
Activity in Deferred Compensation Plan, value		$ 2
Issuance of common stock - RSAs and RSUs, net of canceled awards, shares			222
Issuance of common stock - RSAs and RSUs, 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)
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 - employee stock purchase plan, shares			39
Issuance of common stock - employee stock purchase plan, value		$ 1,083	$ 1,083
Activity in Deferred Compensation Plan, shares		0
Activity in Deferred Compensation Plan, value		$ (2)	$ (2)
Issuance of common stock - RSAs and RSUs, net of canceled awards, shares			(12)
Issuance of common stock - RSAs and RSUs, 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
Shares, Outstanding			71,598
Balance, value at Dec. 31, 2020		2,347,607	$ 1,660,998	575,248	182,195	(70,834)
Net income		159,909		159,909
Other comprehensive income (loss)		(109,478)			(109,478)
Issuance of common stock - employee stock purchase plan, shares			74
Issuance of common stock - employee stock purchase plan, value		2,351	$ 2,351
Activity in Deferred Compensation Plan, shares			0
Activity in Deferred Compensation Plan, value		(8)	$ (8)
Issuance of common stock - RSAs and RSUs, net of canceled awards, shares			178
Issuance of common stock - RSAs and RSUs, net of canceled awards, value		10,835	$ 10,835
Purchase and retirement of common stock, shares			(90)
Purchase and retirement of common stock, value		(4,100)	$ (4,100)
Cash dividends declared on common stock		(83,849)		(83,849)
Balance, value at Sep. 30, 2021		2,323,267	$ 1,670,076	651,308	72,717	(70,834)
Shares, Outstanding			71,742
Balance, value at Jun. 30, 2021		2,333,246	$ 1,664,953	642,018	97,109	(70,834)
Net income		53,017		53,017
Other comprehensive income (loss)		(24,392)			(24,392)
Issuance of common stock - employee stock purchase plan, shares			33
Issuance of common stock - employee stock purchase plan, value		1,253	$ 1,253
Issuance of common stock - RSAs and RSUs, net of canceled awards, shares			(14)
Issuance of common stock - RSAs and RSUs, net of canceled awards, value		3,899	$ 3,899
Purchase and retirement of common stock, shares			1
Purchase and retirement of common stock, value		(29)	$ (29)
Cash dividends declared on common stock	[1]	(43,727)		(43,727)
Balance, value at Sep. 30, 2021		$ 2,323,267	$ 1,670,076	$ 651,308	$ 72,717	$ (70,834)
Shares, Outstanding			71,760

[1] Dividends declared per common share - regular for the three months ended September 30, 2021 includes both the July 29, 2021 declaration of $0.28 and the September 30, 2021 declaration of $0.30.