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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Restricted Stock Units (RSUs) [Member]
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	443	0	0	0
Stock appreciation rights
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	1,919	283	389	489
Performance share units
Antidilutive securities
Number of securities not included in computation of diluted earnings per share (in shares)	685	0	116	0