Capital Stock - Common Stock Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	55,532,307
Common stock, shares outstanding, end of period (shares)	54,882,154	55,532,307
Class A Common Stock
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	0	0	7,167,000
Exercise of stock options/stock appreciation rights (shares)	0	0	0
Director compensation arrangements, net (shares)	0	0	0
Restricted/performance shares activity, net of forfeitures (shares)	0	0	0
Acquisition/surrender of shares (shares)	0	0	0
Share reclassification			(7,167,000)
Common stock, shares outstanding, end of period (shares)	0	0	0
Class B Common Stock
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	0	0	51,329,000
Exercise of stock options/stock appreciation rights (shares)	0	0	29,000
Director compensation arrangements, net (shares)	0	0	17,000
Restricted/performance shares activity, net of forfeitures (shares)	0	0	122,000
Acquisition/surrender of shares (shares)	0	0	(708,000)
Share reclassification			(50,789,000)
Common stock, shares outstanding, end of period (shares)	0	0	0
Common Stock
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	55,532,000	57,837,000	0
Exercise of stock options/stock appreciation rights (shares)	53,000	78,000	0
Director compensation arrangements, net (shares)	10,000	6,000	0
Restricted/performance shares activity, net of forfeitures (shares)	89,000	98,000	0
Acquisition/surrender of shares (shares)	(802,000)	(2,487,000)	(119,000)
Share reclassification			57,956,000
Common stock, shares outstanding, end of period (shares)	54,882,000	55,532,000	57,837,000