Fair Value Measurements - Fair Value Measurements at Reporting Date and Gain (Losses) from Fair Value Changes. (Details) - Non-Recurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 6,500	$ 4,617
Other real estate owned	1,594	2,047
Gain (losses) from fair value changes, Impaired Loans	(173)	(332)
Gain (losses) from fair value changes, Other real estate owned	(211)	(532)
(Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0	0
(Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	6,500	4,617
Other real estate owned	1,594	2,047
(Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	$ 0	$ 0