Financial Information - ASU 2016-13 (Details) - USD ($) $ in Thousands	Mar. 31, 2020		Jan. 01, 2020	Dec. 31, 2019		Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans, net of unearned income	$ 33,378,303	[1]		$ 31,061,111	[1]	$ 27,990,048
Allowance for loan losses	444,490			200,307		$ 184,911	$ 180,424
Other assets	2,536,822			2,046,338
Other liabilities	825,247			873,079
Undivided profits	1,667,105			1,798,442
Total liabilities and equity	$ 47,197,378			$ 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] March 31, 2020 and December 31, 2019 include $20.8 million and $18.8 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate in process of foreclosure.