Fair Value - Impaired Loans Held-for-investment - Tabular Disclosure (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Impaired Loans Held-for-investment
Impaired loans held-for-investment	$ 2,774	$ 3,190
Carried at fair value
Impaired Loans Held-for-investment
Impaired loans held-for-investment	651	1,112
Specific valuation allowance	(290)	(329)
Impaired loans held-for-investment carried at fair value, net	361	783
Portion carried at cost
Impaired Loans Held-for-investment
Impaired loans held-for-investment	$ 2,123	$ 2,078