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Stock-Based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Schedule of Allocated Employee Stock-Based Compensation Expenses | We recorded and allocated employee stock-based compensation expense for our equity incentive plans and our 2000 Employee Stock Purchase Plan (“ESPP”) as follows (in thousands):
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2017 |  | 2016 |  | 2017 |  | 2016
Research and development expense | $ | 1,600 |  |  | $ | 1,165 |  |  | $ | 3,078 |  |  | $ | 6,729 |
Selling, general and administrative expense | 3,427 |  |  | 2,393 |  |  | 6,662 |  |  | 8,014 |
Total stock-based compensation expense | $ | 5,027 |  |  | $ | 3,558 |  |  | $ | 9,740 |  |  | $ | 14,743 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | We use the Black-Scholes Merton option pricing model to value our stock options and ESPP purchases. The weighted average grant-date fair value of our stock options and ESPP purchases was as follows:
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2017 |  | 2016 |  | 2017 |  | 2016
Stock options | $ | 10.07 |  |  | $ | 3.17 |  |  | $ | 10.01 |  |  | $ | 2.67 |
ESPP | $ | 5.65 |  |  | $ | 1.60 |  |  | $ | 4.61 |  |  | $ | 1.79 |
Schedule of Fair Value of Employee Share-Based Payments Awards Estimated Using the Assumptions and Weighted Average Fair Values | The fair value of stock options and ESPP purchases was estimated using the following assumptions:
| Stock Options
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2017 |  | 2016 |  | 2017 |  | 2016
Risk-free interest rate | 1.72 | % |  | 0.90 | % |  | 1.68 | % |  | 1.10 | %
Dividend yield | — | % |  | — | % |  | — | % |  | — | %
Expected volatility | 60 | % |  | 67 | % |  | 61 | % |  | 76 | %
Expected life | 4.3 years |  |  | 4.4 years |  |  | 4.2 years |  |  | 4.4 years |
| ESPP
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2017 |  | 2016 |  | 2017 |  | 2016
Risk-free interest rate | 0.94 | % |  | 0.39 | % |  | 0.77 | % |  | 0.42 | %
Dividend yield | — | % |  | — | % |  | — | % |  | — | %
Expected volatility | 60 | % |  | 65 | % |  | 64 | % |  | 69 | %
Expected life | 6 months |  |  | 6 months |  |  | 6 months |  |  | 6 months |
Summary of All Stock Option Activity | A summary of stock option activity for the six months ended June 30, 2017 is presented below (dollars in thousands, except per share amounts):
| Shares |  | Weighted Average Exercise Price |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
Options outstanding at December 31, 2016 | 24,999,665 |  |  | $ | 4.91 |  |  |  |  |
Granted | 674,110 |  |  | $ | 20.57 |  |  |  |  |
Exercised | (3,242,026 | ) |  | $ | 4.04 |  |  |  |  |
Forfeited | (161,836 | ) |  | $ | 7.27 |  |  |  |  |
Options outstanding at June 30, 2017 | 22,269,913 |  |  | $ | 5.50 |  |  | 4.25 years |  | $ | 426,081 |
Exercisable at June 30, 2017 | 16,181,093 |  |  | $ | 4.13 |  |  | 3.72 years |  | $ | 331,770 |
Summary of All RSU Activity | A summary of restricted stock unit (“RSU”) activity for the six months ended June 30, 2017 is presented below (dollars in thousands, except per share amounts):
| Shares |  | Weighted Average Grant Date Fair Value |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
RSUs outstanding at December 31, 2016 | 2,469,791 |  |  | $ | 8.69 |  |  |  |  |
Awarded | 258,272 |  |  | $ | 20.81 |  |  |  |  |
Vested and released | (280,657 | ) |  | $ | 4.24 |  |  |  |  |
Forfeited | (85,543 | ) |  | $ | 10.72 |  |  |  |  |
RSUs outstanding at June 30, 2017 | 2,361,863 |  |  | $ | 10.47 |  |  | 1.72 years |  | $ | 58,173 |

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -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=27013229&loc=d3e301413-122809 + Details
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- Definition Tabular disclosure of the changes in outstanding nonvested restricted stock units. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the number and weighted-average exercise prices (or conversion ratios) for share options (or share units) that were outstanding at the beginning and end of the year, vested and expected to vest, exercisable or convertible at the end of the year, and the number of share options or share units that were granted, exercised or converted, forfeited, and expired during the year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6415400&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the weighted-average grant-date fair value of equity options or other equity instruments granted during the year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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