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Net Income (Loss) Per Share (Details) - $ / shares	3 Months Ended		6 Months Ended
Net Income (Loss) Per Share (Details) - $ / shares	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income (loss) per share.
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	14,902,000	13,992,000	19,261,000	13,301,000
Convertible Senior Notes Due 2020
Net income (loss) per share.
Net shares issued	0
Minimum stock price to trigger conversion of debt (in dollars per share)	$ 20
Convertible Senior Notes Due 2020 \| Convertible Common Stock
Net income (loss) per share.
Dilutive Securities impact on diluted net income (in dollars per share)	$ 0.00