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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 6,486	$ 6,166	$ 18,034	$ 17,050
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 5,094	$ 4,843	$ 14,165	$ 13,392
Weighted average shares outstanding, basic	3,600,729	3,600,729	3,600,729	3,600,729
Basic earnings per share	$ 1.41	$ 1.35	$ 3.93	$ 3.72
Weighted average shares outstanding, diluted	5,567,909	5,567,909	5,567,909	5,567,909
Diluted earnings per share	$ 1.16	$ 1.11	$ 3.24	$ 3.06
Class B Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 1,392	$ 1,323	$ 3,869	$ 3,658
Weighted average shares outstanding, basic	1,967,180	1,967,180	1,967,180	1,967,180
Basic earnings per share	$ 0.71	$ 0.67	$ 1.97	$ 1.86
Weighted average shares outstanding, diluted	1,967,180	1,967,180	1,967,180	1,967,180
Diluted earnings per share	$ 0.71	$ 0.67	$ 1.97	$ 1.86