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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Summary of Fair Value Assumptions on Stock Options Granted | For the years ended December 31, 2018, 2017 and 2016, the fair value of stock options granted to employees was estimated on the grant date using the Black-Scholes valuation model with the following assumptions:
| 2018 |  | 2017 |  | 2016
Dividend yield | 0 | % |  | 0 | % |  | 0 | %
Expected term (in years) | 5.2 - 6.1 |  |  | 5.3 - 6.3 |  |  | 6.08 |
Risk-free interest rates | 2.5% - 2.9% |  |  | 1.9% - 2.2% |  |  | 1.2% - 2.1% |
Expected volatility | 38% - 45% |  |  | 39% - 43% |  |  | 42% - 45% |
Summary of Activity under Stock Option Plans | The following table summarizes activity under the Company’s stock option plans:
|  | Number of Shares Underlying Outstanding Options |  | Weighted-Average Exercise Price |  | Weighted-Average Remaining Contractual Term (Years) |  | Aggregate Intrinsic Value (in thousands)
Balances at January 1, 2016 |  | 20,710,510 |  |  | $ | 2.79 |  |  | 8.28 |  | $ | 8,634 |
Granted |  | 2,624,450 |  |  | 3.20 |  |  |  |  |
Exercised |  | (272,591 | ) |  | 0.99 |  |  |  |  |
Forfeited and canceled |  | (2,132,867 | ) |  | 2.93 |  |  |  |  |
Balances at December 31, 2016 |  | 20,929,502 |  |  | 2.85 |  |  | 7.58 |  | 11,149 |
Granted |  | 5,803,596 |  |  | 3.58 |  |  |  |  |
Exercised |  | (1,554,944 | ) |  | 1.64 |  |  |  |  |
Forfeited and canceled |  | (1,570,408 | ) |  | 2.98 |  |  |  |  |
Balances at December 31, 2017 |  | 23,607,746 |  |  | 3.10 |  |  | 7.39 |  | 22,260 |
Granted |  | 4,468,523 |  |  | 5.88 |  |  |  |  |
Exercised |  | (3,522,631 | ) |  | 2.32 |  |  |  |  |
Forfeited and canceled |  | (779,359 | ) |  | 3.80 |  |  |  |  |
Balances at December 31, 2018 |  | 23,774,279 |  |  | 3.71 |  |  | 7.10 |  | 342,262 |
Vested and exercisable as of December 31, 2018 |  | 13,774,468 |  |  | 3.19 |  |  | 6.13 |  | 205,455 |
Vested and expected to vest as of December 31, 2018 |  | 23,774,279 |  |  | 3.71 |  |  | 7.10 |  | 342,262 |
Summary of Activity under RSU Plans | The following table summarizes the RSU activity and related information under the 2018 EIP:
| Number of RSUs Outstanding |  | Weighted-Average Grant Date Fair Value
Unvested balance - January 1, 2018 | — |  |  | $ | — |
Granted | 327,202 |  |  | 15.00 |
Vested | (38,742 | ) |  | 15.00 |
Forfeited/canceled | — |  |  | — |
Unvested balance - December 31, 2018 | 288,460 |  |  | $ | 15.00 |
Summary of Fair Value Assumptions on Employee Stock Purchas Plans | For the year ended December 31, 2018, the assumptions used to determine the fair value of the shares to be awarded are as follows:
| 2018
Dividend yield | 0 | %
Expected term (in years) | 0.5 - 2.0 |
Risk-free interest rates | 2.4% - 2.9% |
Unvested balance - expected volatility | 37 | %
Summary of Components of Stock-Based Compensation Expense Recognized | The following table summarizes the components of stock-based compensation expense recognized in the consolidated statements of operations for the years ended December 31, 2018, 2017 and 2016 (in thousands):
| 2018 |  | 2017 |  | 2016
Cost of revenue | $ | 282 |  |  | $ | 290 |  |  | $ | 193 |
Research and development | 3,258 |  |  | 1,797 |  |  | 1,820 |
Sales and marketing | 1,637 |  |  | 1,299 |  |  | 1,052 |
General and administrative | 5,184 |  |  | 3,460 |  |  | 4,201 |
Total | $ | 10,361 |  |  | $ | 6,846 |  |  | $ | 7,266 |

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- Definition Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + 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 employee stock purchase plans, including, but not limited to: (a) expected term, (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 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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