Statement of Comprehensive Income (Statement) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Attributable to Parent	$ 127,923	$ 102,700	$ 110,387
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	928	1,487	1,075
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	8,675	(1,511)	4,046
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax, Total	7,747	(2,998)	2,971
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	2,596	(333)	(2,024)
Other Comprehensive Income (Loss), Transfers from Held-to-maturity to Available-for-Sale Securities, Net of Tax	0	19,095	0
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	25,747	18,227	(17,586)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax	23,151	37,655	(15,562)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax	(244)	(454)	0
Other Comprehensive Income (Loss), Net of Tax	15,160	40,199	(18,533)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest, Total	$ 143,083	$ 142,899	$ 91,854