Common Stock and Earnings per Share - Schedule of Earnings per Share, Basic (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class A Non-Voting
Numerator:
Allocation of undistributed earnings	$ (392)	$ 6,941	$ 7,821
Dividends paid	8,592	8,639	8,780
Net income available to common shareholders, basic	$ 8,200	$ 15,580	$ 16,601
Denominator:
Weighted-average common shares outstanding, basic (in shares)	30,637	30,805	31,322
Earnings per share - basic (in usd per share)	$ 0.27	$ 0.51	$ 0.53
Class B Voting
Numerator:
Allocation of undistributed earnings	$ (294)	$ 5,509	$ 6,144
Dividends paid	4,579	4,889	4,920
Net income available to common shareholders, basic	$ 4,285	$ 10,398	$ 11,064
Denominator:
Weighted-average common shares outstanding, basic (in shares)	22,975	24,449	24,606
Earnings per share - basic (in usd per share)	$ 0.19	$ 0.43	$ 0.45