Shareholders' Equity and Other Comprehensive Income (Loss) (Changes in Accumulated Other Comprehensive Income (Loss) by Component (Net of Income Taxes)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	$ 5,065,205	$ 4,597,753	$ 4,941,690	$ 3,133,602
Other comprehensive income (loss), Net of Tax Amount	(53,941)	67,631	137,329	143,709
Balance	5,052,968	4,753,816	5,052,968	4,753,816
Accumulated other comprehensive income (loss)	(202,970)		(202,970)		$ (65,641)
Total
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	256,911	(18,342)	65,641	(94,420)
Other comprehensive income (loss) before reclassifications	(2,309)	66,290	195,523	142,453
Amounts reclassified from AOCI	(51,632)	1,341	(58,194)	1,256
Other comprehensive income (loss), Net of Tax Amount	(53,941)	67,631	137,329	143,709
Balance	202,970	49,289	202,970	49,289
Net unrealized gains (losses) on investment securities available for sale
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	194,524	(7,071)	83,666	(83,179)
Other comprehensive income (loss) before reclassifications	(8,847)	66,290	108,484	142,453
Amounts reclassified from AOCI	(51,432)	1,367	(57,905)	1,312
Other comprehensive income (loss), Net of Tax Amount	(60,279)	67,657	50,579	143,765
Balance	134,245	60,586	134,245	60,586
Net unrealized gains (losses) on investment securities available for sale | Valuation Allowance of Deferred Tax Assets
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Accumulated other comprehensive income (loss)	13,300		13,300
Net unrealized gains (losses) on cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	61,925	(12,137)	(18,487)	(12,137)
Other comprehensive income (loss) before reclassifications	6,538	0	87,039	0
Amounts reclassified from AOCI	(200)	0	(289)	0
Other comprehensive income (loss), Net of Tax Amount	6,338	0	86,750	0
Balance	68,263	(12,137)	68,263	(12,137)
Post-retirement unfunded health benefit
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	462	866	462	896
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI	0	(26)	0	(56)
Other comprehensive income (loss), Net of Tax Amount	0	(26)	0	(56)
Balance	462	$ 840	462	$ 840
Net unrealized losses on cash flow hedges | Valuation Allowance of Deferred Tax Assets
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Accumulated other comprehensive income (loss)	$ 12,100		$ 12,100