Description of Business and Basis of Presentation (Anti-dilutive Shares) (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Outstanding options to purchase common stock
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	364	465
Unvested restricted stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	29	96
Unvested restricted stock unit awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	2,760	1,686
Employee stock purchase plan awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	29	61
Bonus to be paid in stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	349	183
Convertible senior notes
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	6,300	0