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Stock-based Compensation - Additional Information (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Number of shares exercised | 54,720 |
Unamortized stock-based compensation cost related to unvested stock options | $ 707 |
Unamortized stock-based compensation cost, weighted average period of recognition | 3 years |
2012 Equity Incentive Plan |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Number of shares available to be issued | 459,075 |
Expiration period | 10 years |
Number of shares exercised | 0 | 0
2012 Equity Incentive Plan | Minimum |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Vesting period | 2 years |
2012 Equity Incentive Plan | Maximum |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Vesting period | 4 years |
2012 Equity Incentive Plan | Options and SARs | Minimum |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Exercise price options granted from fair value common stock, percent | 100.00% |
2012 Equity Incentive Plan | Granted to Ten Percent Stockholders | Minimum |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Exercise price options granted from fair value common stock, percent | 110.00% |
2012 Equity Incentive Plan | Granted to Ten Percent Stockholders | Maximum |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Vesting period | 5 years |

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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested options awarded to employees as compensation. + 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 (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (a)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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