Capital Stock (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Class A Common Stock
Class of Stock [Line Items]
Common Stock, Shares, Outstanding	38,461,948		38,169,575
Stock repurchased and retired (in shares)	0	0
Class B Common Stock
Class of Stock [Line Items]
Common Stock, Shares, Outstanding	22,374,171		22,453,672