Condensed Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock Voting and Nonvoting Common Stock	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss
Balance, beginning of period at Dec. 31, 2018	$ 288,735		$ 227,587	$ 77,689		$ (16,541)
Balance, beginning of period (Accounting Standards Update 2017-08) at Dec. 31, 2018		$ (821)			$ (821)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,143			18,143
Other comprehensive income (loss)	(514)					(514)
Dividends declared	(1,829)			(1,829)
Recognition of the fair value of share-based compensation	1,278		1,278
Repurchase of common stock	(9,784)		(9,784)
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	26		26
Common stock redeemed for the net settlement of share-based awards	(94)		(94)
Balance, end of period at Sep. 30, 2019	295,140		219,013	93,182		(17,055)
Balance, beginning of period at Jun. 30, 2019	296,120		224,244	87,454		(15,578)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,326			6,326
Other comprehensive income (loss)	(1,477)					(1,477)
Dividends declared	(598)			(598)
Recognition of the fair value of share-based compensation	416		416
Repurchase of common stock	(5,651)		(5,651)
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	4		4
Balance, end of period at Sep. 30, 2019	295,140		219,013	93,182		(17,055)
Balance, beginning of period at Dec. 31, 2019	304,913		219,423	99,681		(14,191)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,362			18,362
Other comprehensive income (loss)	(4,899)					(4,899)
Dividends declared	(1,802)			(1,802)
Recognition of the fair value of share-based compensation	1,600		1,600
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	21		21
Common stock redeemed for the net settlement of share-based awards	(93)		(93)
Balance, end of period at Sep. 30, 2020	318,102		220,951	116,241		(19,090)
Balance, beginning of period at Jun. 30, 2020	307,711		220,418	108,431		(21,138)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,411			8,411
Other comprehensive income (loss)	2,048					2,048
Dividends declared	(601)			(601)
Recognition of the fair value of share-based compensation	527		527
Deferred stock rights and restricted stock units issued in lieu of cash dividends payable on outstanding deferred stock rights and restricted stock units	6		6
Balance, end of period at Sep. 30, 2020	$ 318,102		$ 220,951	$ 116,241		$ (19,090)