Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 64,964	$ 39,559	$ 138,027	$ 65,606
Other Comprehensive Income (Loss), net of tax:
Unrealized gain (loss) on securities	19,298	34,424	(20,701)	51,853
Reclassification adjustment for securities (gains) losses included in net income	(28)	(2,341)	349	(2,376)
Amortization of net unrealized (gains) losses on AFS securities transferred to HTM	(270)	793	1,517	1,589
Net unrealized gain on interest rate swaps used in cash flow hedges	2,074	0	367	0
Amortization of net unrecognized pension and postretirement income	289	255	578	510
Other Comprehensive Income (Loss)	21,363	33,131	(17,890)	51,576
Total Comprehensive Income	$ 86,327	$ 72,690	$ 120,137	$ 117,182