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 2016-02 [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	51,210		51,210
Other comprehensive income (loss)	140,710			140,710
Issuance of common stock - employee stock purchase plan, shares		26
Issuance of common stock - employee stock purchase plan, value	$ 945	$ 945
Activity in Deferred Compensation Plan, shares	0
Activity in Deferred Compensation Plan, value	$ 4
Issuance of common stock - RSAs and RSUs, net of canceled awards, shares		234
Issuance of common stock - RSAs and RSUs, net of canceled awards, value	4,909	$ 4,909
Purchase and retirement of common stock, shares		(67)
Purchase and retirement of common stock, value	(2,482)	$ (2,482)
Cash dividends declared on common stock	(56,046)		(56,046)
Purchase of treasury stock, shares		(731)
Purchase of treasury stock, value	(20,000)				(20,000)
Balance, value at Jun. 30, 2020	2,276,755	$ 1,654,129	512,383	181,077	(70,834)
Shares, Outstanding		71,575
Balance, value at Mar. 31, 2020	2,213,602	$ 1,651,399	495,830	137,207	(70,834)
Net income	36,582		36,582
Other comprehensive income (loss)	$ 43,870			43,870
Activity in Deferred Compensation Plan, shares	0
Activity in Deferred Compensation Plan, value	$ 1	$ 1
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	2,737	$ 2,737
Purchase and retirement of common stock, shares		(1)
Purchase and retirement of common stock, value	(8)	$ (8)
Cash dividends declared on common stock	(20,029)		(20,029)
Balance, value at Jun. 30, 2020	2,276,755	$ 1,654,129	512,383	181,077	(70,834)
Shares, Outstanding		71,586
Shares, Outstanding		71,598
Balance, value at Dec. 31, 2020	2,347,607	$ 1,660,998	575,248	182,195	(70,834)
Net income	106,892		106,892
Other comprehensive income (loss)	(85,086)			(85,086)
Issuance of common stock - employee stock purchase plan, shares		41
Issuance of common stock - employee stock purchase plan, value	1,098	$ 1,098
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		192
Issuance of common stock - RSAs and RSUs, net of canceled awards, value	6,936	$ 6,936
Purchase and retirement of common stock, shares		(89)
Purchase and retirement of common stock, value	(4,071)	$ (4,071)
Cash dividends declared on common stock	(40,122)		(40,122)
Balance, value at Jun. 30, 2021	2,333,246	$ 1,664,953	642,018	97,109	(70,834)
Shares, Outstanding		71,739
Balance, value at Mar. 31, 2021	2,275,063	$ 1,661,129	607,040	77,728	(70,834)
Net income	55,039		55,039
Other comprehensive income (loss)	19,381			19,381
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		4
Issuance of common stock - RSAs and RSUs, net of canceled awards, value	3,908	$ 3,908
Purchase and retirement of common stock, shares		1
Purchase and retirement of common stock, value	(76)	$ (76)
Cash dividends declared on common stock	(20,061)		(20,061)
Balance, value at Jun. 30, 2021	$ 2,333,246	$ 1,664,953	$ 642,018	$ 97,109	$ (70,834)
Shares, Outstanding		71,742