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, 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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,900		21,900
Other comprehensive income (loss)	(10,459)			(10,459)
Cash dividends declared	(2,377)		(2,377)
Net cash proceeds from common stock issuance	54,334	54,334
Repurchase of common stock	(216)	(216)
Recognition of the fair value of share-based compensation	1,596	1,596
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	40	40
Common stock redeemed for the net settlement of share-based awards	(210)	(210)
Balance at Dec. 31, 2018	288,735	227,587	77,689	(16,541)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings	77,689
Net income	25,239		25,239
Other comprehensive income (loss)	2,350			2,350
Cash dividends declared	(2,426)		(2,426)
Repurchase of common stock	(9,784)	(9,784)
Recognition of the fair value of share-based compensation	1,680	1,680
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	34	34
Common stock redeemed for the net settlement of share-based awards	(94)	(94)
Balance at Dec. 31, 2019	304,913	$ 219,423	$ 99,681	$ (14,191)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings	$ 99,681