Description of Business and Basis of Presentation (Anti-dilutive Shares) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	10,998	2,925
Outstanding options to purchase common stock
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	328	352
Unvested restricted stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	14	58
Unvested restricted stock unit awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	3,261	2,356
Employee stock purchase plan awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	41	57
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	109	102
Convertible senior notes
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	7,245	0