Financial Information - ASU 2016-13 (Details) - USD ($) $ in Thousands	Jun. 30, 2020		Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019		Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans, net of unearned income	$ 32,708,937	[1]			$ 31,061,111	[1]	$ 29,712,810
Allowance for loan losses	537,881		$ 444,490		200,307		$ 192,749	$ 184,911	$ 180,424
Other assets	2,209,235				2,046,338
Other liabilities	900,884				873,079
Undivided profits	1,671,629				1,798,442
Total liabilities and equity	$ 48,644,659				$ 43,310,900
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans, net of unearned income				$ 2,980
Allowance for loan losses				(106,394)
Other assets (deferred taxes)				31,330
Other assets				(72,084)
Other liabilities				23,973
Undivided profits				(96,057)
Total liabilities and equity				$ (72,084)

[1] June 30, 2020 and December 31, 2019 include $16.9 million and $18.8 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate in process of foreclosure.