Allowance for Credit Losses (Components of Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	$ 321,209	$ 379,910	$ 253,412	$ 158,461
Allowance for held-to-maturity securities losses	99	59	70
Allowance for credit losses	321,308	379,969	253,482
Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	277,709	319,374	216,050
Unfunded lending-related commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	43,500	60,536	37,362
Loan losses and unfunded lending-related commitments losses
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	$ 321,209	$ 379,910	$ 253,412