Loans and Allowance for Losses and Concentrations of Credit Risk - Troubled Debt Restructurings (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) defaulted_loan	Sep. 30, 2015 USD ($) defaulted_loan	Sep. 30, 2016 USD ($) defaulted_loan	Sep. 30, 2015 USD ($) defaulted_loan
Receivables [Abstract]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Number Defaulted | defaulted_loan	3	1	8	3
Payments to Acquire Other Loans and Leases Held-for-investment	$ 1,102,000	$ 263,000	$ 2,516,000	$ 2,244,000
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	0	0	1,100,000
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 1,100,000
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Subsequent Default, Determination of Allowance for Credit Losses	0	0