Earnings 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	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 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)					9,373,666	9,335,154	9,329,514	9,264,227
Weighted average number of net shares issued (redeemed) (shares)	(22,223)	(4,596)	40,123	64,144
Weighted average shares outstanding (basic) (shares)	9,351,443	9,324,918	9,375,277	9,328,371
Weighted average of potential dilutive shares attributable to stock options granted, computed under the treasury stock method (shares)	4,245	3,559	4,067	4,874
Weighted average number of shares (diluted) (shares)	9,355,688	9,328,477	9,379,344	9,333,245
Net income (In thousands)	$ 10,050	$ 8,552	$ 30,971	$ 23,883
Earnings per share:
Basic (in dollars per share)	$ 1.07	$ 0.92	$ 3.30	$ 2.56
Diluted (in dollars per share)	$ 1.07	$ 0.92	$ 3.30	$ 2.56