Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 1) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) Loan Region	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Financing Receivable Impaired [Line Items]
Accrued interest receivable	$ 37,400
Maximum concentration of loan as a percentage of total LHFI	10.00%
Key market regions | Region	5
Number of days to pass to be classified as past due LHFI	30 days
Minimum loan amount for loan to be specifically reviewed for impairment and deemed impaired			$ 500
LHFI classified as TDRs	$ 25,400	$ 30,500
LHFI classified as TDRs from credits with interest only payments and credits renewed at a rate that was not commensurate with that of new debt with similar risk	13,300	20,200
Unused commitments on TDRs	4,200	7,900
Financing receivable, related allowance	2,600	2,900
Financing receivable, related charge-offs	$ 2,300	$ 472
Number of individual loans modified as per CARES Act | Loan	2,812
Aggregate principal balances of loans modified as per CARES Act	$ 1,327,000
Period of extension on interest part of loans modified as per CARES Act	90 days
Period of extension on full payment deferrals part of loans modified as per CARES Act	90 days
Commercial Credits [Member]
Financing Receivable Impaired [Line Items]
Number of days past due for loan to be classified as nonaccrual	90 days
Non-Business Purpose Credits [Member]
Financing Receivable Impaired [Line Items]
Number of days past due for loan to be classified as nonaccrual	120 days