Capital Stock, Repurchases of Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2015
Repurchases of Common Stock [Abstract]
Class A common stock repurchased	$ 144,334	$ 825	$ 69,565
2015 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Authorized amount					$ 500,000
2018 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Authorized amount				$ 500,000
Amount available for repurchases	325,800
Treasury Stock [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased	$ 144,334	$ 825	$ 69,565
Treasury Stock [Member] | 2015 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased (in shares)			500,000
Class A common stock repurchased			$ 40,600
Treasury Stock [Member] | 2018 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased (in shares)	5,100,000	14,000	400,000
Class A common stock repurchased	$ 144,300	$ 800	$ 29,000