Stockholders' Equity - Summary of Shares Issued and Held in Treasury or Outstanding (Detail) - shares	Jun. 30, 2019	Dec. 31, 2018
Class A Common Stock [Member]
Class of Stock [Line Items]
Common stock - issued	17,112,722	17,064,138
Common stock - held in treasury	(1,548,849)	(1,271,043)
Common stock - outstanding	15,563,873	15,793,095
Class B Common Stock [Member]
Class of Stock [Line Items]
Common stock - issued	234,903	234,903
Common stock - held in treasury	(234,903)	(234,903)
Common stock - outstanding	0	0