Net Loss per Share (Details) - shares shares in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Net Loss per Share
Amounts excluded from the calculation of diluted net loss per share due to their anti-dilutive effect	12,645	7,625
Outstanding stock awards and Employee Stock Purchase Plan
Net Loss per Share
Amounts excluded from the calculation of diluted net loss per share due to their anti-dilutive effect	7,366	7,068
Unvested restricted stock units
Net Loss per Share
Amounts excluded from the calculation of diluted net loss per share due to their anti-dilutive effect	1,093	537
Shares issuable upon conversion of Convertible Notes
Net Loss per Share
Amounts excluded from the calculation of diluted net loss per share due to their anti-dilutive effect	4,186	20

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Antidilution
-URI http://asc.fasb.org/extlink&oid=6505113

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Diluted Earnings Per Share
-URI http://asc.fasb.org/extlink&oid=6510752

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Contingent Stock Agreement
-URI http://asc.fasb.org/extlink&oid=6508534

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration