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)
Balance, value at Dec. 31, 2019	$ 2,159,962	$ 1,650,753	519,676	$ 40,367	$ (50,834)
Net income	14,628		14,628
Other comprehensive income (loss)	96,840			96,840
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	$ 3	$ 3
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	2,172	$ 2,172
Purchase and retirement of common stock, shares		(66)
Purchase and retirement of common stock, value	(2,474)	$ (2,474)
Cash dividends declared on common stock	(36,017)		(36,017)
Purchase of treasury stock, shares		(731)
Purchase of treasury stock, value	(20,000)				(20,000)
Balance, value at Mar. 31, 2020	2,213,602	$ 1,651,399	495,830	137,207	(70,834)
Shares, Outstanding		71,575
Shares, Outstanding		71,598
Balance, value at Dec. 31, 2020	2,347,607	$ 1,660,998	575,248	182,195	(70,834)
Net income	51,853		51,853
Other comprehensive income (loss)	(104,467)			(104,467)
Issuance of common stock - employee stock purchase plan, shares		41
Issuance of common stock - employee stock purchase plan, value	1,098	$ 1,098
Issuance of common stock - RSAs and RSUs, net of canceled awards, shares		188
Issuance of common stock - RSAs and RSUs, net of canceled awards, value	3,028	$ 3,028
Purchase and retirement of common stock, shares		88
Purchase and retirement of common stock, value	(3,995)	$ (3,995)
Cash dividends declared on common stock	(20,061)		(20,061)
Balance, value at Mar. 31, 2021	$ 2,275,063	$ 1,661,129	$ 607,040	$ 77,728	$ (70,834)
Shares, Outstanding		71,739