Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Aug. 03, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Dividends declared (in dollars per share)		$ 0.52	$ 0.51	$ 1.04	$ 1.02
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance, Beginning of Period				$ 335,868	$ 104,923
Net change in unrealized gain (loss)		$ 8,480	$ 56,922	(141,651)	354,765
Reclassification Adjustments Included in Earnings [Abstract]
Gain on available for sale securities, net		(1,430)	(5,580)	(1,897)	(5,583)
Other comprehensive income, before income taxes		7,050	51,342	(143,548)	349,182
Federal and state income taxes		1,691	12,318	(34,448)	83,789
Other comprehensive income, net of income taxes		5,359	39,024	(109,100)	265,393
Balance, End of Period		226,768	370,316	226,768	370,316
Accumulated Net Unrealized Gain (Loss) on Available for Sale Securities [Member]
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance, Beginning of Period				335,032	104,996
Net change in unrealized gain (loss)				(141,651)	354,765
Reclassification Adjustments Included in Earnings [Abstract]
Gain on available for sale securities, net				(1,897)	(5,583)
Other comprehensive income, before income taxes				(143,548)	349,182
Federal and state income taxes				(34,448)	83,789
Other comprehensive income, net of income taxes				(109,100)	265,393
Balance, End of Period		225,932	370,389	225,932	370,389
Accumulated Unrealized Gain (Loss) on Employee Benefit Plans [Member]
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance, Beginning of Period				836	(73)
Net change in unrealized gain (loss)				0	0
Reclassification Adjustments Included in Earnings [Abstract]
Gain on available for sale securities, net				0	0
Other comprehensive income, before income taxes				0	0
Federal and state income taxes				0	0
Other comprehensive income, net of income taxes				0	0
Balance, End of Period		$ 836	$ (73)	$ 836	$ (73)
Subsequent Event [Member]
Dividends Payable, Date Declared	Aug. 03, 2021
Dividends declared (in dollars per share)	$ 0.52
Dividends Payable, Date to be Paid	Aug. 26, 2021
Dividends Payable, Date of Record	Aug. 16, 2021