Description of Business and Basis of Presentation (Anti-dilutive Shares) (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	11,199	9,831
Outstanding options to purchase common stock
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	357	364
Unvested restricted stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	0	29
Unvested restricted stock unit awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	3,016	2,760
Employee stock purchase plan awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	77	29
Bonus and director fees to be paid in stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	504	349
Convertible senior notes
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	7,245	6,300