Common Stock and Earnings per Share - Schedule of Earnings (Loss) Per Share, Diluted (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	$ (394)	$ 7,003	$ 7,911
Dividends paid	8,592	8,639	8,780
Net income available to common shareholders, diluted	$ 8,198	$ 15,642	$ 16,691
Denominator:
Weighted-average common shares outstanding, basic (in shares)	30,637	30,805	31,322
Weighted-average effect of dilutive securities (in shares)	453	629	836
Weighted-average number of shares outstanding, diluted (in shares)	31,090	31,434	32,158
Earnings per share - diluted (in usd per share)	$ 0.26	$ 0.50	$ 0.52
Class B Voting
Numerator:
Allocation of undistributed earnings	$ (292)	$ 5,447	$ 6,053
Dividends paid	4,579	4,889	4,920
Net income available to common shareholders, diluted	$ 4,287	$ 10,336	$ 10,973
Denominator:
Weighted-average common shares outstanding, basic (in shares)	22,975	24,449	24,606
Weighted-average effect of dilutive securities (in shares)	0	0	0
Weighted-average number of shares outstanding, diluted (in shares)	22,975	24,449	24,606
Earnings per share - diluted (in usd per share)	$ 0.19	$ 0.42	$ 0.45