3. Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 9,221	$ 7,971	$ 26,506	$ 27,947
Weighted average basic shares outstanding	1,853	1,852	1,853	1,844
Add: Effect of dilutive securities	5	5	4	12
Weighted average diluted shares outstanding	1,858	1,857	1,857	1,856
Earnings per share:
Basic	$ 4.98	$ 4.3	$ 14.3	$ 15.16
Diluted	$ 4.96	$ 4.29	$ 14.27	$ 15.06