Capital Stock - Common Stock Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	54,882,154
Common stock, shares outstanding, end of period (shares)	54,715,188	54,882,154
Common Stock
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	54,882,000	55,532,000	57,837,000
Exercise of stock options/stock appreciation rights (shares)	66,000	53,000	78,000
Director compensation arrangements, net (shares)	11,000	10,000	6,000
Restricted/performance shares activity, net of forfeitures (shares)	165,000	89,000	98,000
Acquisition/surrender of shares (shares)	(409,000)	(802,000)	(2,487,000)
Common stock, shares outstanding, end of period (shares)	54,715,000	54,882,000	55,532,000