Earnings Per Share - Potentially Dilutive Shares Excluded From Dilutive EPS Calculation (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Convertible Senior Notes Maturing May 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	8,997	8,997	1,475
Convertible Senior Notes Maturing September 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	10,344	0	0
Convertible Senior Notes Maturing March 2032
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	524	2,403	6,891