Common Stock and Treasury Stock - Additional Information (Details) - Stock Buy back Program [Member] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Common Stock [Line Items]
Stock Repurchased During Period, Shares	0		0
Class A Common Stock
Common Stock [Line Items]
Share repurchase program, authorized amount	$ 75,800,000		$ 75,800,000
Stock repurchase program, remaining authorization amount	$ 18,800,000		$ 18,800,000
Stock Repurchased During Period, Shares		800		1,600
Stock Repurchased During Period, Value		$ 21,000		$ 41,000