Net Income (Loss) Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	9,889,523	10,327,975	9,923,098	14,067,376
2019 Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	0	3,045,781	0	4,225,737
2036 Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	8,937,353	7,282,194	8,937,353	9,841,639
Stock appreciation rights
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	952,170	0	985,745	0