Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	May 04, 2021	Mar. 31, 2021	Mar. 31, 2020
Dividends declared (in dollars per share)		$ 0.52	$ 0.51
Schedule of Accumulated Other Income (Loss) [Abstract]
Balance, Beginning of Period		$ 335,868	$ 104,923
Net change in unrealized gain (loss)		(150,131)	297,843
Reclassification Adjustments Included in Earnings [Abstract]
Gain on available for sale securities, net		(467)	(3)
Other comprehensive income, before income taxes		(150,598)	297,840
Federal and state income taxes		(36,139)	71,471
Other comprehensive income, net of income taxes		(114,459)	226,369
Balance, End of Period		221,409	331,292
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)		(150,131)	297,843
Reclassification Adjustments Included in Earnings [Abstract]
Gain on available for sale securities, net		(467)	(3)
Other comprehensive income, before income taxes		(150,598)	297,840
Federal and state income taxes		(36,139)	71,471
Other comprehensive income, net of income taxes		(114,459)	226,369
Balance, End of Period		220,573	331,365
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)
Subsequent Event [Member]
Dividends Payable, Date Declared	May 04, 2021
Dividends declared (in dollars per share)	$ 0.52
Dividends Payable, Date to be Paid	May 27, 2021
Dividends Payable, Date of Record	May 17, 2021