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
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	$ 4,941,690	$ 3,133,602
Other comprehensive income (loss), Net of Tax Amount	191,270	76,078
Balance	5,065,205	4,597,753
Accumulated other comprehensive income (loss)	(256,911)		$ (65,641)
Total
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	65,641	(94,420)
Other comprehensive income (loss) before reclassifications	197,831	76,164
Amounts reclassified from AOCI	(6,561)	(86)
Other comprehensive income (loss), Net of Tax Amount	191,270	76,078
Balance	256,911	(18,342)
Net unrealized gains (losses) on investment securities available for sale
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	83,666	(83,179)
Other comprehensive income (loss) before reclassifications	117,330	76,164
Amounts reclassified from AOCI	(6,472)	(56)
Other comprehensive income (loss), Net of Tax Amount	110,858	76,108
Balance	194,524	(7,071)
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
Net unrealized gains (losses) on cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	(18,487)	(12,137)
Other comprehensive income (loss) before reclassifications	80,501	0
Amounts reclassified from AOCI	(89)	0
Other comprehensive income (loss), Net of Tax Amount	80,412	0
Balance	61,925	(12,137)
Post-retirement unfunded health benefit
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	462	896
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	0	(30)
Other comprehensive income (loss), Net of Tax Amount	0	(30)
Balance	462	$ 866
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