Loans Held for Investment and Allowance for Loan Losses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originations of loans held for investment, modified			$ 13,730	$ 6,672
Proceeds from sale of previously charged-off loans	$ 1,900	$ 900	3,800	1,900
Allowance for loan losses for non-delinquent loans	70,200		70,200		$ 59,500
Allowance for loan losses for delinquent loans	35,000		35,000		50,700
Reserve for Off-balance Sheet Activities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Related accrual for unfunded loan commitments	4,100		4,100		3,900
Unused lines of Credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Off-balance sheet credit exposure	185,100		185,100		$ 164,500
Financial Institutions Borrower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originations of loans held for investment, modified	$ 120,700	$ 130,200	$ 265,700	$ 233,700