Reconciliation of Basic and Diluted Shares - Antidilutive Securities Excluded from Computation of Earnings per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Restricted Stock Units (RSUs) [Member]
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	0	739	0	744
Stock appreciation rights
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	467	2,472	656	2,558
Performance share units
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	690	896	851	918