Unaudited Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings- Substantially Restricted	Accumulated Other Compre- hensive (Loss) Income
Balance, beginning (in shares) at Dec. 31, 2020		95,426,364
Balance, beginning at Dec. 31, 2020	$ 2,307,041	$ 954	$ 1,495,053	$ 667,944	$ 143,090
Increase (Decrease) in Stockholders' Equity
Net income	234,048			234,048
Other comprehensive loss	(65,431)				(65,431)
Cash dividends declared	(90,929)			(90,929)
Stock issuances under stock incentive plans (in shares)		86,295
Stock issuances under stock incentive plans	0	$ 1	(1)
Stock-based compensation and related taxes	2,887		2,887
Balance, ending (in shares) at Sep. 30, 2021		95,512,659
Balance, ending at Sep. 30, 2021	2,387,616	$ 955	1,497,939	811,063	77,659
Balance, beginning (in shares) at Jun. 30, 2021		95,507,234
Balance, beginning at Jun. 30, 2021	2,353,955	$ 955	1,496,488	766,070	90,442
Increase (Decrease) in Stockholders' Equity
Net income	75,619			75,619
Other comprehensive loss	(12,783)				(12,783)
Cash dividends declared	(30,626)			(30,626)
Stock issuances under stock incentive plans (in shares)		5,425
Stock-based compensation and related taxes	1,451		1,451
Balance, ending (in shares) at Sep. 30, 2021		95,512,659
Balance, ending at Sep. 30, 2021	$ 2,387,616	$ 955	1,497,939	811,063	77,659
Balance, beginning (in shares) at Dec. 31, 2021	110,687,533	110,687,533
Balance, beginning at Dec. 31, 2021	$ 3,177,622	$ 1,107	2,338,814	810,342	27,359
Increase (Decrease) in Stockholders' Equity
Net income	223,525			223,525
Other comprehensive loss	(522,507)				(522,507)
Cash dividends declared	(109,922)			(109,922)
Stock issuances under stock incentive plans (in shares)		79,421
Stock issuances under stock incentive plans	0	$ 1	(1)
Stock-based compensation and related taxes	$ 3,639		3,639
Balance, ending (in shares) at Sep. 30, 2022	110,766,954	110,766,954
Balance, ending at Sep. 30, 2022	$ 2,772,357	$ 1,108	2,342,452	923,945	(495,148)
Balance, beginning (in shares) at Jun. 30, 2022		110,766,287
Balance, beginning at Jun. 30, 2022	2,896,239	$ 1,108	2,341,097	881,246	(327,212)
Increase (Decrease) in Stockholders' Equity
Net income	79,338			79,338
Other comprehensive loss	(167,936)				(167,936)
Cash dividends declared	(36,639)			(36,639)
Stock issuances under stock incentive plans (in shares)		667
Stock-based compensation and related taxes	$ 1,355		1,355
Balance, ending (in shares) at Sep. 30, 2022	110,766,954	110,766,954
Balance, ending at Sep. 30, 2022	$ 2,772,357	$ 1,108	$ 2,342,452	$ 923,945	$ (495,148)