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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2017
Accounting Policies [Abstract] |
Summary of Fair Value Measurement Financial Assets | Financial assets measured at fair value on a recurring basis were as follows (in thousands):
| Fair Value Measurement at December 31, 2017
|  |  | Quoted Prices in Active Markets for Identical Assets |  | Significant Other Observable Inputs |  | Significant Unobservable Inputs
| Total |  | Level 1 |  | Level 2 |  | Level 3
Assets: |  |  |  |  |  |  |
Money market funds | $ | 61,512 |  |  | $ | 61,512 |  |  | $ | — |  |  | $ | — |
U.S Treasury securities | 3,990 |  |  | — |  |  | 3,990 |  |  | — |
Government-sponsored enterprises | 11,990 |  |  | — |  |  | 11,990 |  |  | — |
Corporate debt securities | 78,418 |  |  | — |  |  | 78,418 |  |  | — |
Total assets measured at fair value (a) | $ | 155,910 |  |  | $ | 61,512 |  |  | $ | 94,398 |  |  | $ | — |
(a) Total assets measured at fair value at December 31, 2017 includes approximately $62.5 million reported in cash and cash equivalents on the balance sheet.
| Fair Value Measurement at December 31, 2016
|  |  | Quoted Prices in Active Markets for Identical Assets |  | Significant Other Observable Inputs |  | Significant Unobservable Inputs
| Total |  | Level 1 |  | Level 2 |  | Level 3
Assets: |  |  |  |  |  |  |
Money market funds | $ | 46,781 |  |  | $ | 46,781 |  |  | $ | — |  |  | $ | — |
U.S Treasury securities | 8,826 |  |  | — |  |  | 8,826 |  |  | — |
Government-sponsored enterprises | 29,759 |  |  | — |  |  | 29,759 |  |  | — |
Corporate debt securities | 166,300 |  |  | — |  |  | 166,300 |  |  | — |
Total assets measured at fair value (a) | $ | 251,666 |  |  | $ | 46,781 |  |  | $ | 204,885 |  |  | $ | — |
(a) Total assets measured at fair value at December 31, 2016 includes approximately $50.8 million reported in cash and cash equivalents on the balance sheet.
Summary of Percentage of Customer Concentration | The following table includes those collaborators that represent more than 10% of total revenue earned in the periods indicated:
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
Incyte Corporation (Incyte) | 96% |  | * |  | *
Janssen Biotech, Inc. (Janssen) | * |  | 85% |  | 72%
Boehringer Ingelheim GmbH (Boehringer) | * |  | * |  | 12%
The following table includes those counterparties that represent more than 10% of accounts receivable at the date indicated:
| December 31,
| 2017 |  | 2016
F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche) | 73% |  | *
Les Laboratoires Servier and Institut de Recherches Servier (Servier) | 12% |  | 31%
Janssen | * |  | 40%
U.S. Government | * |  | 19%
* Balance is less than 10%
Estimated Useful Lives | Depreciation and amortization are computed using the straight-line method over the following estimated useful lives:
Computer equipment | 3 years
Software | 3 years
Furniture | 10 years
Laboratory and office equipment | 5 years
Leasehold improvements | Shorter of lease term or useful life
Computation of Basic and Diluted Loss Per Common Share | Basic and diluted loss per common share is computed as follows (in thousands except share and per share data):
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
Numerator: |  |  |  |  |
Net loss used for calculation of basic and diluted EPS | $ | (19,626 | ) |  | $ | (58,528 | ) |  | $ | (20,140 | )
Denominator: |  |  |  |  |
Weighted average shares outstanding, basic | 36,095,080 |  |  | 34,685,274 |  |  | 31,801,645 |
Effect of dilutive securities: |  |  |  |  |
Stock options and restricted stock units | — |  |  | — |  |  | — |
Weighted average shares outstanding, diluted | 36,095,080 |  |  | 34,685,274 |  |  | 31,801,645 |
Net loss per share, basic and diluted | $ | (0.54 | ) |  | $ | (1.69 | ) |  | $ | (0.63 | )
Schedule of Antidilutive Securities Excluded from the Calculation of Diluted Loss Per Share | The following common stock equivalents were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive:
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
Stock options | 4,504,642 |  |  | 3,838,060 |  |  | 4,146,064 |

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- Definition Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2C -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL7498348-110258 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258 + Details
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