Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 1)	12 Months Ended
	Dec. 31, 2019 USD ($) Region	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounts Notes Loans And Financing Receivable Gross Allowance And Net [Abstract]
Maximum concentration of loan as a percentage of total LHFI	10.00%
Key market regions | Region	5
Loans and Leases Receivable, Related Parties	$ 35,500,000	$ 49,000,000.0
New loan advances to related party	464,600,000
Loan repayment by related party	478,100,000
Loan increase (decreases) from changes in executive officers and directors	0
Minimum loan amount for loan to be specifically reviewed for impairment and deemed impaired	500,000
LHFI Classified as TDRs	31,500,000	28,200,000	$ 23,900,000
LHFI classified as TDRs from credits with interest only payments	20,800,000	23,800,000	20,500,000
Unused Commitments on TDRs	7,000,000.0	4,400,000	0
Financing receivable, related allowance	3,200,000	2,300,000	458,000
Financing receivable, related charge-offs	$ 1,600,000	$ 18,400,000	$ 127,000