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 Income (loss)
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	158,429			158,429
Other comprehensive loss	(52,648)				(52,648)
Cash dividends declared	(60,303)			(60,303)
Stock issuances under stock incentive plans (in shares)		80,870
Stock issuances under stock incentive plans	0	$ 1	(1)
Stock-based compensation and related taxes	1,436		1,436
Balance, ending (in shares) at Jun. 30, 2021		95,507,234
Balance, ending at Jun. 30, 2021	2,353,955	$ 955	1,496,488	766,070	90,442
Balance, beginning (in shares) at Mar. 31, 2021		95,501,819
Balance, beginning at Mar. 31, 2021	2,295,385	$ 955	1,495,438	719,072	79,920
Increase (Decrease) in Stockholders' Equity
Net income	77,627			77,627
Other comprehensive loss	10,522				10,522
Cash dividends declared	(30,629)			(30,629)
Stock issuances under stock incentive plans (in shares)		5,415
Stock issuances under stock incentive plans	0	$ 0	0
Stock-based compensation and related taxes	1,050		1,050
Balance, ending (in shares) at Jun. 30, 2021		95,507,234
Balance, ending at Jun. 30, 2021	$ 2,353,955	$ 955	1,496,488	766,070	90,442
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	144,187			144,187
Other comprehensive loss	(354,571)				(354,571)
Cash dividends declared	(73,283)			(73,283)
Stock issuances under stock incentive plans (in shares)		78,754
Stock issuances under stock incentive plans	0	$ 1	(1)
Stock-based compensation and related taxes	$ 2,284		2,284
Balance, ending (in shares) at Jun. 30, 2022	110,766,287	110,766,287
Balance, ending at Jun. 30, 2022	$ 2,896,239	$ 1,108	2,341,097	881,246	(327,212)
Balance, beginning (in shares) at Mar. 31, 2022		110,763,316
Balance, beginning at Mar. 31, 2022	2,934,193	$ 1,108	2,339,405	841,489	(247,809)
Increase (Decrease) in Stockholders' Equity
Net income	76,392			76,392
Other comprehensive loss	(79,403)				(79,403)
Cash dividends declared	(36,635)			(36,635)
Stock issuances under stock incentive plans (in shares)		2,971
Stock issuances under stock incentive plans	0	$ 0	0
Stock-based compensation and related taxes	$ 1,692		1,692
Balance, ending (in shares) at Jun. 30, 2022	110,766,287	110,766,287
Balance, ending at Jun. 30, 2022	$ 2,896,239	$ 1,108	$ 2,341,097	$ 881,246	$ (327,212)