Capital Stock - Common Stock Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	54,514,172
Common stock, shares outstanding, end of period (shares)	54,382,659	54,514,172
Common Stock
Common Stock, Shares, Outstanding [Roll Forward]
Common stock, shares outstanding, beginning of period (shares)	54,514,000	54,715,000	54,882,000
Exercise of stock options/stock appreciation rights (shares)	87,000	84,000	66,000
Director compensation arrangements, net (shares)	9,000	10,000	11,000
Restricted/performance shares activity, net of forfeitures (shares)	132,000	39,000	165,000
Acquisition/surrender of shares (shares)	(359,000)	(334,000)	(409,000)
Common stock, shares outstanding, end of period (shares)	54,383,000	54,514,000	54,715,000