Parent Company Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest and Dividend Income, Operating	$ 91,800	$ 89,566	$ 87,445	$ 88,909	$ 91,829	$ 94,589	$ 92,226	$ 81,856	$ 357,720	$ 360,500	$ 310,801
Interest Expense	5,479	5,726	6,259	12,626	14,820	17,488	16,375	14,080	30,090	62,763	43,903
Income taxes									26,722	22,071	20,912
Net Income (Loss) Attributable to Parent	$ 45,200	$ 30,846	$ 29,505	$ 22,372	$ 23,936	$ 31,146	$ 22,163	$ 25,455	127,923	102,700	110,387
Other Comprehensive Income (Loss), Net of Tax									15,160	40,199	(18,533)
Parent Company
Dividends From Subsidiaries									97,000	97,500	100,000
Interest and Dividend Income, Operating									1,250	1,250	1,275
Other Income									98	4,634	6,068
Revenues									98,348	103,384	107,343
Interest Expense									4,311	1,950	617
Other Expenses									12,234	19,804	14,619
Operating Expenses									16,545	21,754	15,236
Income Before Taxes And Equity In Undistributed Losses Of Subsidiaries									81,803	81,630	92,107
Income taxes									(4,390)	(4,242)	(4,010)
Income Before Equity In Undistributed Losses Of Subsidiaries									86,193	85,872	96,117
Equity In Undistributed Losses Of Subsidiaries									(41,730)	(16,828)	(14,270)
Net Income (Loss) Attributable to Parent									127,923	102,700	110,387
Other Comprehensive Income (Loss), Net of Tax									15,160	40,199	(18,533)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									$ 143,083	$ 142,899	$ 91,854