Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock Voting and Nonvoting Common Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2014	$ 96,785	$ 71,774	$ 25,146	$ (135)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,929		8,929
Other comprehensive income (loss)	(1,074)			(1,074)
Cash dividends declared	(1,095)		(1,095)
Recognition of the fair value of share-based compensation	762	762
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	25	25
Excess tax benefit on share-based compensation	36	36
Common stock redeemed for the net settlement of share-based awards	(38)	(38)
Balance at Dec. 31, 2015	104,330	72,559	32,980	(1,209)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,074		12,074
Other comprehensive income (loss)	(8,059)			(8,059)
Cash dividends declared	(1,350)		(1,350)
Net cash proceeds from common stock issuance	46,223	46,223
Recognition of the fair value of share-based compensation	736	736
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	30	30
Excess tax benefit on share-based compensation	49	49
Common stock redeemed for the net settlement of share-based awards	(91)	(91)
Balance at Dec. 31, 2016	153,942	119,506	43,704	(9,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,226		15,226
Other comprehensive income (loss)	4,249			4,249
Cash dividends declared	(1,827)		(1,827)
Net cash proceeds from common stock issuance	51,636	51,636
Recognition of the fair value of share-based compensation	1,038	1,038
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	36	36
Common stock redeemed for the net settlement of share-based awards	(173)	(173)
Balance at Dec. 31, 2017	$ 224,127	$ 172,043	$ 57,103	$ (5,019)