Capital Stock (Details 3) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock units
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	0	810	0
Stock options
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	52	89	98
Stock Appreciation Rights (SARs)
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	811	1,458	1,142
Performance Shares [Member]
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	201	684	278