Description of Business and Basis of Presentation (Anti-dilutive Shares) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Outstanding options to purchase common stock
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	352	907
Unvested restricted stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	58	216
Unvested restricted stock unit awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	2,356	1,773
Employee stock purchase plan awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	57	90
Bonus to be paid in stock awards
Schedule of anti-dilutive shares excluded from computation of net loss per share
Anti-dilutive, shares	102	104