Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Class A Common Stock [Member]	Retained Earnings [Member] Class B Common Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2017	$ 260,297	$ 3,606	$ 1,962	$ 12,292	$ 263,666			$ (21,229)
Net income	36,213				36,213
Other comprehensive income, net of tax:
Unrealized holding gains arising during period, net of taxes	109							109
Accretion of net unrealized losses transferred during the period, net of taxes	1,086							1,086
Pension liability adjustment, net of taxes	4,937							4,937
Adoption of ASU 2018-2, Income Statement-Reporting Comprehensive Income (Topic 220)-Reclassification of Certain Tax Effects from AOCI					3,783			(3,783)
Adoption of ASU 2016-1, Financial Instruments-Overall (Subtopic 825-10) Recognition and Measurement of Financial Assets and Financial Liabilities					29			(29)
Conversion of Class B Common Stock to Class A Common Stock		2	(2)
Cash dividends		(1,732)	(471)			$ (1,732)	$ (471)
Ending balance at Dec. 31, 2018	300,439	3,608	1,960	12,292	301,488			(18,909)
Net income	39,699				39,699
Other comprehensive income, net of tax:
Unrealized holding gains arising during period, net of taxes	(314)							(314)
Accretion of net unrealized losses transferred during the period, net of taxes	753							753
Pension liability adjustment, net of taxes	(5,789)							(5,789)
Conversion of Class B Common Stock to Class A Common Stock		43	(43)
Cash dividends		(1,742)	(465)			(1,742)	(465)
Ending balance at Dec. 31, 2019	332,581	3,651	1,917	12,292	338,980			(24,259)
Net income	42,209				42,209
Other comprehensive income, net of tax:
Unrealized holding gains arising during period, net of taxes	438							438
Accretion of net unrealized losses transferred during the period, net of taxes	591							591
Pension liability adjustment, net of taxes	(2,920)							(2,920)
Conversion of Class B Common Stock to Class A Common Stock		5	(5)
Cash dividends		(1,973)	(517)			$ (1,973)	$ (517)
Ending balance at Dec. 31, 2020	$ 370,409	$ 3,656	$ 1,912	$ 12,292	$ 378,699			$ (26,150)