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

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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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

No definition available.

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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

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Represents the annual increase in maximum number of shares (or other type of equity) approved (usually by shareholders and board of directors), for awards under the equity-based compensation plan.

+ References

No definition available.

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- Definition

Represents the annual percentage increase in maximum number of shares (or other type of equity) approved (usually by shareholders and board of directors), for awards under the equity-based compensation plan.

+ References

No definition available.

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Stock Based Compensation (Details) - shares		6 Months Ended
Stock Based Compensation (Details) - shares	Dec. 02, 2013	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Stock-based compensation
Common stock, shares issued		55,821,310		47,002,488
Employee stock options
Stock-based compensation
Options granted (in shares)		1,553,400	1,356,100
ESPP
Stock-based compensation
Total number of shares of common stock available for issuance		581,286
Awards issued under the plan (in shares)		318,945
Annual increase in shares of common stock available for issuance (in shares)		0
ESPP \| Maximum
Stock-based compensation
Annual percentage increase in shares of common stock available for issuance		1.00%
Annual increase in shares of common stock available for issuance (in shares)		621,814
Restricted stock units
Stock-based compensation
Vesting period		3 years
The 2013 Plan
Stock-based compensation
Total number of shares of common stock available for issuance		10,009,294
Annual percentage increase in shares of common stock available for issuance		4.00%
Awards issued under the plan (in shares)		6,498,750
Increase in shares of common stock available for issuance (in shares)		1,880,100
The 2010 Plan
Stock-based compensation
Total number of shares of common stock available for issuance		2,684,456
Options granted (in shares)	0