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Stock-based Compensation (Tables) | 3 Months Ended
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Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Weighted Average Assumptions | The fair value of the stock options granted during the three months ended March 31, 2019 and 2018, was estimated based on the following weighted average assumptions:
| Three Months Ended March 31, |  |
| 2019 |  |  | 2018 |  |
Dividend yield |  | 0 | % |  |  | 0 | % |
Expected volatility |  | 103 | % |  |  | 101 | % |
Risk-free interest rate |  | 2.55 | % |  |  | 2.72 | % |
Expected term | 5.60 years |  |  | 5.60 years |  |
Stock Option Activity | Stock option activity for the three months ended March 31, 2019, was as follows:
| Number of shares |  |  | Weighted Average Exercise Price Per Share |  |  | Weighted Average Contractual Term (in years) |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding at beginning of year |  | 1,624,746 |  |  | $ | 23.09 |  |  |  |  |  |  |  |  |
Granted |  | 349,979 |  |  |  | 14.23 |  |  |  |  |  |  |  |  |
Exercised |  | (23,861 | ) |  |  | 4.83 |  |  |  |  |  |  |  |  |
Forfeited, expired or cancelled |  | (32,914 | ) |  |  | 64.36 |  |  |  |  |  |  |  |  |
Outstanding at end of period |  | 1,917,950 |  |  | $ | 20.99 |  |  |  | 7.9 |  |  | $ | 7,624 |
Exercisable at end of period |  | 1,134,601 |  |  | $ | 24.42 |  |  |  | 7.1 |  |  | $ | 6,046 |
Stock-based Compensation Expense | The following table shows total stock-based compensation expense for stock options, RSUs and ESPP in the condensed consolidated statements of operations and comprehensive income (loss) (in thousands):
| Three Months Ended March 31, |  |
| 2019 |  |  | 2018 |  |
Research and development | $ | 49 |  |  | $ | 104 |  |
General and administrative |  | 1,679 |  |  |  | 1,312 |  |
Total stock-based compensation expense | $ | 1,728 |  |  | $ | 1,416 |  |

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- Definition Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 + Details
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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