Basis of Presentation (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ 3,264,295		$ 917,227
Assets:
Allowance for debt securities held to maturity losses	15,105	$ 15,017	0
Allowance for loan losses	$ 1,804,423	$ 1,754,352	920,993	$ 942,191	$ 977,660	$ 885,242
Liabilities:
Allowance for credit losses on letters of credit and unfunded commitments			66,955
As Reported Under ASC 326
Assets:
Allowance for debt securities held to maturity losses			1,847
Allowance for loan losses			1,105,924
Liabilities:
Allowance for credit losses on letters of credit and unfunded commitments			76,946
Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit			150,200
Assets:
Allowance for debt securities held to maturity losses			1,847
Allowance for loan losses			184,931
Liabilities:
Allowance for credit losses on letters of credit and unfunded commitments			$ 9,991