Earnings 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	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Summary of computation of basic and diluted earnings per share [Abstract]
Common shares outstanding at the beginning of the period (shares)					9,378,414	9,335,154	9,337,397	9,264,227
Weighted average number of net shares issued (redeemed) (shares)	(4,470)	(2,552)	52,041	65,871
Weighted average shares outstanding (basic) (shares)	9,373,944	9,334,845	9,387,195	9,330,098
Weighted average of potential dilutive shares attributable to stock options granted, computed under the treasury stock method (shares)	4,162	4,551	3,996	5,299
Weighted average number of shares (diluted) (shares)	9,378,106	9,339,396	9,391,191	9,335,397
Net income (In thousands)	$ 10,063	$ 6,457	$ 20,921	$ 15,331
Earnings per share:
Basic (in dollars per share)	$ 1.07	$ 0.69	$ 2.23	$ 1.64
Diluted (in dollars per share)	$ 1.07	$ 0.69	$ 2.23	$ 1.64