Earnings Per Share ("EPS") - Reconciliation of Basic EPS and Diluted EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 11,732	$ 10,887	$ 33,325	$ 30,609
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 9,326	$ 8,630	$ 26,452	$ 24,254
Weighted average shares outstanding, basic	3,672,969	3,655,469	3,663,669	3,653,429
Basic earnings per share	$ 2.54	$ 2.36	$ 7.22	$ 6.64
Net income	$ 9,326	$ 8,630	$ 26,452	$ 24,254
Weighted average shares outstanding, diluted	5,567,909	5,567,909	5,567,909	5,567,909
Diluted earnings per share	$ 2.11	$ 1.96	$ 5.99	$ 5.50
Class B Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 2,406	$ 2,257	$ 6,873	$ 6,355
Weighted average shares outstanding, basic	1,894,940	1,912,440	1,904,240	1,914,480
Basic earnings per share	$ 1.27	$ 1.18	$ 3.61	$ 3.32
Net income	$ 2,406	$ 2,257	$ 6,873	$ 6,355
Weighted average shares outstanding, diluted	1,894,940	1,912,440	1,904,240	1,914,480
Diluted earnings per share	$ 1.27	$ 1.18	$ 3.61	$ 3.32