Allowance for Credit Losses and Credit Quality - Narrative (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Recorded Investment, Past Due
Allowance for credit loss		$ 549,181	$ 116,580	$ 158,874	$ 172,520
Percentage of allowance for credit loss to total loans and leases		0.0159
Commitments to lend additional funds		$ 2,600
Minimum period of loans delinquent to be considered in default		90 days
Other real estate owned and repossessed and returned assets, write down		$ 2,600	7,700	$ 3,400
Consumer real estate
Financing Receivable, Recorded Investment, Past Due
Maximum period past due for accruing status for consumer real estate troubled debt restructuring loans	90 days
Leasing and Equipment Finance
Financing Receivable, Recorded Investment, Past Due
Commitments to lend additional funds			$ 638