Common Stock and Treasury Stock - Information Relating to the Number of Shares of Our Common Stock Issued (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Class A Common Stock
Common Stock [Line Items]
Balance, shares	6,771	6,732	6,771	6,732
Conversion of shares				13
Issuance of restricted stock				29
Forfeiture of restricted stock (in shares)	(2)	(2)	(2)	(3)
Balance, shares	6,769	6,730	6,769	6,771
Class B Common Stock
Common Stock [Line Items]
Balance, shares	954	923	954	923
Conversion of shares				(13)
Issuance of restricted stock				44
Forfeiture of restricted stock (in shares)	0	0	0	0
Balance, shares	954	923	954	954