Common Stock and Treasury Stock (Details) - shares shares in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Common Stock [Line Items]
Exercise of stock options	29,035
Class A Common Stock [Member]
Common Stock [Line Items]
Balance, shares	6,638	6,603
Exercise of stock options	21
Conversion of shares	4	12
Forfeiture of restricted stock	(1)
Issuance of restricted stock		23
Balance, shares	6,662	6,638
Class B Common Stock [Member]
Common Stock [Line Items]
Balance, shares	878	865
Exercise of stock options	8
Conversion of shares	(4)	(12)
Forfeiture of restricted stock	0
Issuance of restricted stock		25
Balance, shares	882	878