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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Restricted Stock Units (RSUs) [Member]
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	0	691	0	723
Stock appreciation rights
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	842	2,383	719	2,499
Performance share units
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	1,004	857	902	894