Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast period to estimate expected credit losses	4 years
Term to estimate expected credit losses determined by macroeconomics variable	3 years
Additional term to estimated expected credit losses determined by microeconomics variable diminishing	1 year
Measurement period of historical losses, pro rata period	1 year
Allowance for loan and lease losses	$ 988,102	$ 537,881	$ 200,307	$ 193,149	$ 192,749	$ 180,424
Consumer real estate | Commercial, Financial, and Industrial (a)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted average life	3 years
HELOC and R/E Installment Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted average life	5 years
COVID-19 Deferrals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan and lease losses	$ 1,100