Stockholders' Equity - Additional Information (Detail) - shares	12 Months Ended			65 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Jul. 18, 2013
Equity, Class of Treasury Stock [Line Items]
Minimum percentage of class A common stock declared dividend excess over class B dividend	10.00%
Class A Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury stock	3,002,588			3,002,588
Class B Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury stock		72,465
Stock Repurchase Program Two [Member] | Class A Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Authority to purchase shares					500,000
Common stock shares purchased	0	0	0	57,658