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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	$ 5,052,968	$ 4,753,816	$ 4,941,690	$ 3,133,602
Other comprehensive income (loss), Net of Tax Amount	(28,056)	26,644	109,273	170,353
Balance	5,064,542	4,868,838	5,064,542	4,868,838
Accumulated other comprehensive income (loss)	(174,914)		(174,914)		$ (65,641)
Total
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	202,970	49,289	65,641	(94,420)
Other comprehensive income (loss) before reclassifications	(28,441)	23,879	167,082	166,332
Amounts reclassified from AOCI	385	2,765	(57,809)	4,021
Other comprehensive income (loss), Net of Tax Amount	(28,056)	26,644	109,273	170,353
Balance	174,914	75,933	174,914	75,933
Net unrealized gains (losses) on investment securities available for sale
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	134,245	60,586	83,666	(83,179)
Other comprehensive income (loss) before reclassifications	(21,806)	25,133	86,678	167,586
Amounts reclassified from AOCI	1,149	2,765	(56,756)	4,077
Other comprehensive income (loss), Net of Tax Amount	(20,657)	27,898	29,922	171,663
Balance	113,588	88,484	113,588	88,484
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	68,263	(12,137)	(18,487)	(12,137)
Other comprehensive income (loss) before reclassifications	(6,635)	(876)	80,404	(876)
Amounts reclassified from AOCI	(764)	0	(1,053)	0
Other comprehensive income (loss), Net of Tax Amount	(7,399)	(876)	79,351	(876)
Balance	60,864	(13,013)	60,864	(13,013)
Post-retirement unfunded health benefit
Changes in Accumulated Other Comprehensive Income (Loss) by Component [Roll Forward]
Balance	462	840	462	896
Other comprehensive income (loss) before reclassifications	0	(378)	0	(378)
Amounts reclassified from AOCI	0	0	0	(56)
Other comprehensive income (loss), Net of Tax Amount	0	(378)	0	(434)
Balance	462	$ 462	462	$ 462
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