Capital Stock, Repurchases of Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2018	Oct. 31, 2015	Aug. 31, 2013	Dec. 31, 1998
Repurchases of Common Stock [Abstract]
Class A common stock repurchased	$ 825	$ 69,565	$ 71,731
1998 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Authorized amount							$ 10,000
Increase in authorized amount						$ 400,000
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	470,200
Treasury Stock [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased	$ 825	$ 69,565	$ 71,731
Treasury Stock [Member] | 2015 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased (in shares)		500,000	1,200,000
Class A common stock repurchased		$ 40,600	$ 71,700
Treasury Stock [Member] | 2018 Stock Repurchase Plan [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased (in shares)	14,000	400,000
Class A common stock repurchased	$ 800	$ 29,000