Reconciliation of Basic and Diluted Shares - Antidilutive Securities Excluded from Computation of Earnings per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock options
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	0	55	0	55
Stock appreciation rights
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	75	526	349	918
Performance share units
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	0	0	0	212