Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

+ References

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ 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 (a)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

+ References

No definition available.

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Stock Incentive Plans - Employee Stock Purchase Plan (Details) - shares			1 Months Ended	12 Months Ended
	Jan. 01, 2018	Jan. 01, 2017	Jun. 30, 2015	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation
Common Stock, Issued, (in shares)				23,645,247	18,817,572
2015 Plan
Stock-Based Compensation
Shares available for grant (in shares)				1,068,287
2015 Plan \| Annual minimum increase
Stock-Based Compensation
Shares available for grant (in shares)				1,297,334
Percentage of outstanding Common Stock available for issuance (as a percent)				4.00%
Potential increase in shares available for issuance as determined by the Board of Directors (in shares)	945,810	752,702
Common Stock \| 2015 ESPP
Stock-Based Compensation
Common Stock, Issued, (in shares)				0
Shares available for grant (in shares)			182,352
Common Stock \| 2015 ESPP \| Annual minimum increase
Stock-Based Compensation
Percentage of outstanding Common Stock available for issuance (as a percent)			1.00%
Potential increase in shares available for issuance as determined by the Board of Directors (in shares)	236,452	188,175	364,705