Capital Stock - Changes in Outstanding Common Stock (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in Common Stock [Roll Forward]
Outstanding, beginning of year (in shares)	106,697	106,363	104,572
Shares issued for exercise of options (in shares)	0	281	603
Shares issued for time vested restricted stock (net of forfeitures) (in shares)	740	53	1,188
Shares issued for employee stock purchase plan (in shares)	151	0	0
Outstanding, end of year (in shares)	107,588	106,697	106,363