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
-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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Net Loss Per Common Share (Anti-Dilutive Common Share Equivalents) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	11,410,980	15,580,272	12,874,565
Warrants to purchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	1,985,846	1,985,846
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	7,918,853	11,426,296	10,711,321
Common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	2,007,846
Common stock \| Warrants to purchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	22,000	22,000	309,792
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	3,342,640	3,888,768	1,853,452
Employee stock purchase program
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common share equivalents (in shares)	127,487	243,208	0
Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Price of shares entitled to purchase (in dollars per share)	$ 10.70