Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 1) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) Region	Jun. 30, 2018 USD ($)	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	$ 52,900		$ 61,600
Nonaccrual	52,888		61,624
Minimum loan amount for loan to be specifically reviewed for impairment and deemed impaired	500
LHFI classified as TDRs	36,300	$ 34,500
LHFI classified as TDRs from credits with interest only payments	25,700	21,800
Unused commitments on TDRs	2,300	0
Financing receivable, related allowance	2,900	9,100
Financing receivable, related charge-offs	117	300
Troubled Debt Restructurings [Member]
Financing Receivable Impaired [Line Items]
Nonaccrual	$ 21,399	$ 33,218	$ 16,700