Earnings Per Share (Details 2) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and restricted stock-based awards	7,419	7,482	3,884
Convertible Notes due 2017 [Member] | Convertible debt [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and restricted stock-based awards	5,702	14,295	15,682
Convertible Notes due 2021 [Member] | Convertible debt [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and restricted stock-based awards	0	0	0
Common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Share price (in dollars per share)	$ 8.80