Summary of Significant Accounting Policies (New Accounting Pronouncements Adopted) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements Adopted and Recent Accounting Pronouncements [Line Items]
Allowance for loan losses	$ 619,983		$ 358,287	$ 311,322	$ 287,128
Retained earnings	$ 4,000,414		$ 3,689,377
Accounting Standards Update 2016-13
New Accounting Pronouncements Adopted and Recent Accounting Pronouncements [Line Items]
Allowance for loan losses		$ 125,200
Retained earnings		98,000
Accounting Standards Update 2016-13 | Unfunded Loan Commitment
New Accounting Pronouncements Adopted and Recent Accounting Pronouncements [Line Items]
Allowance for loan losses		$ 10,500