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Stock-Based Compensation (Tables) | 3 Months Ended
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Mar. 29, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Allocated Employee Stock-Based Compensation Expense | We allocated the stock-based compensation expense for our equity incentive plans and our 2000 Employee Stock Purchase Plan (ESPP) as follows (in thousands):
| Three Months Ended March 31,
| 2019 |  | 2018
Research and development | $ | 4,306 |  |  | $ | 3,033 |
Selling, general and administrative | 8,223 |  |  | 6,272 |
Total stock-based compensation | $ | 12,529 |  |  | $ | 9,305 |
Weighted Average Grant-Date Fair Value of Stock Options and ESPP Purchases | The weighted average grant-date fair value per share of stock options and ESPP purchases were as follows:
| Three Months Ended March 31,
| 2019 |  | 2018
Stock options | $ | 9.21 |  |  | $ | 11.52 |
ESPP | $ | 4.67 |  |  | $ | 7.39 |
Valuation Assumptions Used to Estimate Grant-Date Fair Value | The grant-date fair value of stock option grants and ESPP purchases was estimated using the following assumptions:
| Three Months Ended March 31,
| 2019 |  | 2018
Stock options: |  |  |
Risk-free interest rate | 2.22 | % |  | 2.40 | %
Dividend yield | — | % |  | — | %
Volatility | 49 | % |  | 54 | %
Expected life | 4.0 years |  |  | 4.0 years |
ESPP: |  |  |
Risk-free interest rate | 2.48 | % |  | 1.53 | %
Dividend yield | — | % |  | — | %
Volatility | 57 | % |  | 53 | %
Expected life | 6 months |  |  | 6 months |
Stock Option Activity | Activity for stock options during the three months ended March 31, 2019 was as follows (dollars in thousands, except per share amounts):
| Shares |  | Weighted Average Exercise Price Per Share |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
Options outstanding at December 31, 2018 | 22,674,062 |  |  | $ | 8.71 |  |  |  |  |
Granted | 246,820 |  |  | $ | 22.94 |  |  |  |  |
Exercised | (1,413,766 | ) |  | $ | 4.91 |  |  |  |  |
Forfeited | (44,200 | ) |  | $ | 14.32 |  |  |  |  |
Expired | (22,925 | ) |  | $ | 22.12 |  |  |  |  |
Options outstanding at March 31, 2019 | 21,439,991 |  |  | $ | 9.10 |  |  | 3.6 years |  | $ | 317,143 |
Exercisable at March 31, 2019 | 15,714,721 |  |  | $ | 6.01 |  |  | 2.9 years |  | $ | 280,307 |
RSU Activity | Activity for RSUs during the three months ended March 31, 2019 was as follows (dollars in thousands, except per share amounts):
| Shares |  | Weighted Average Grant Date Fair Value Per Share |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
RSUs outstanding at December 31, 2018 | 4,857,334 |  |  | $ | 18.42 |  |  |  |  |
Awarded | 123,410 |  |  | $ | 22.94 |  |  |  |  |
Vested and released | (194,296 | ) |  | $ | 7.83 |  |  |  |  |
Forfeited | (100,630 | ) |  | $ | 18.13 |  |  |  |  |
RSUs outstanding at March 31, 2019 | 4,685,818 |  |  | $ | 18.98 |  |  | 2.0 years |  | $ | 111,522 |

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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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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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