Fair Value - Impaired Loans Held-for-investment - Additional Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Impaired Loans Held-for-investment
Impaired loans held-for-investment	$ 2,774	$ 3,190
Additional provision (credit) for loan losses	254	320
Partial charge-offs	0	0
Carrying amount
Impaired Loans Held-for-investment
Foreclosed assets	0	229
Carried at fair value
Impaired Loans Held-for-investment
Impaired loans held-for-investment	651	1,112
Specific valuation allowance	290	329
Portion carried at cost
Impaired Loans Held-for-investment
Impaired loans held-for-investment	$ 2,123	$ 2,078