Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 1) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) Region	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable Impaired [Line Items]
Maximum concentration of loan as a percentage of total LHFI	10.00%
Key market regions | Region	5
Carrying amounts of nonaccrual LHFI considered for impairment analysis	$ 59,000		$ 61,600
Nonaccrual	59,030		61,624
Minimum loan amount for loan to be specifically reviewed for impairment and deemed impaired	500
LHFI classified as TDRs	30,500	$ 36,000
LHFI classified as TDRs from credits with interest only payments	20,200	24,700
Unused commitments on TDRs	7,900	7,700
Financing receivable, related allowance	2,900	14,300
Financing receivable, related charge-offs	472	4,700
Troubled Debt Restructurings [Member]
Financing Receivable Impaired [Line Items]
Nonaccrual	$ 29,163	$ 33,617	$ 16,700