Stockholders' equity (deficit) and redeemable convertible preferred stock Common stock (Details) - shares	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common Stock, Shares Authorized	500,000,000.0
Common Class A [Member]
Class of Stock [Line Items]
Common Stock, Shares Authorized	500,000,000	500,000,000
Common Stock, Shares, Issued	100,596,000	52,091,000
Common Class B [Member]
Class of Stock [Line Items]
Common Stock, Shares Authorized	150,000,000	150,000,000
Common Stock, Shares, Issued	36,005,000	77,023,000

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.

No definition available.

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- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

+ References

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 30
-Article 5

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- Definition

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.

+ References

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