3. Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 8,797	$ 10,026	$ 17,285	$ 19,976
Weighted average basic shares outstanding	1,852	1,844	1,853	1,839
Add: Effect of dilutive securities	5	14	3	17
Weighted average diluted shares outstanding	1,857	1,858	1,856	1,856
Earnings per share:
Basic	$ 4.75	$ 5.44	$ 9.33	$ 10.86
Diluted	$ 4.74	$ 5.40	$ 9.31	$ 10.76