Fair Value - Impaired Loans Held-for-investment - Additional Disclosures (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Impaired Loans Held-for-investment
Impaired loans held-for-investment	$ 26,810	$ 2,774
Additional provision (credit) for loan losses	7,288	254
Carrying amount
Impaired Loans Held-for-investment
Foreclosed assets	0	0
Carried at fair value
Impaired Loans Held-for-investment
Impaired loans held-for-investment	14,616	651
Specific valuation allowance	7,464	290
Portion carried at cost
Impaired Loans Held-for-investment
Impaired loans held-for-investment	$ 12,194	$ 2,123