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Stockholders' Equity - Award Modifications (Details) - USD ($) shares in Millions |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 30, 2016 | Mar. 31, 2018 | Dec. 31, 2016 | Dec. 31, 2018
2016 Plan Modification |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Plan modification, stock-based compensation | $ 18,800,000 |  | $ 8,900,000 |
Allocated share-based compensation expense |  |  | $ 37,700,000 |
Plan modification, remaining unamortized expense |  |  |  | $ 0
Restricted Stock Units (RSUs) |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Plan modification, stock-based compensation |  | $ 10,000,000 |  |
Restricted Stock Units (RSUs) | 2016 Plan Modification |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
RSUs received on exchange (in shares) |  |  | 2.2 |
Employee Stock Option | 2016 Plan Modification |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Stock options exchanged (in shares) |  |  | 4.3 |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: 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 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 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition An excess of the fair value of the modified award over the fair value of the award immediately before the modification. + 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)(2)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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