Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 1) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Region	Mar. 31, 2018 USD ($)	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	$ 56,400		$ 61,600
Nonaccrual	56,423		61,624
Minimum loan amount for loan to be specifically reviewed for impairment and deemed impaired	500
LHFI classified as TDRs	30,200	$ 25,800
LHFI classified as TDRs from credits with interest only payments	24,800	22,700
Unused commitments on TDRs	4,400	0
Financing receivable, related allowance	2,800	4,500
Financing receivable, related charge-offs	43	0
Troubled Debt Restructurings [Member]
Financing Receivable Impaired [Line Items]
Nonaccrual	$ 16,388	$ 25,786	$ 16,700