Net Loss per Share (Details) - shares	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Anti-Dilutive Securities
Anti-dilutive securities (in shares)	10,597,000	10,088,000
Share issuances under equity incentive plan and ESPP
Anti-Dilutive Securities
Anti-dilutive securities (in shares)	3,916,000	3,386,000
RSAs
Anti-Dilutive Securities
Anti-dilutive securities (in shares)	5,000	26,000
Shares issuances upon the conversion of convertible senior notes
Anti-Dilutive Securities
Anti-dilutive securities (in shares)	6,676,000	6,676,000
Performance-based vesting
Anti-Dilutive Securities
Anti-dilutive securities (in shares)	1,305,000	1,305,000

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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration