Employee Benefits and Share-Based Compensation - Stock Award Plans (Details) shares in Thousands	12 Months Ended
Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)	7,835
2009 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance (in shares)	5,500
2009 Plan \| Vesting one year from the vesting commencement date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of award vesting	25.00%
2009 Plan \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	4 years
Shares reserved for future issuance (in shares)	3,323
2009 Plan \| Employee Stock Option \| Vesting one year from the vesting commencement date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	1 year
2009 Plan \| Employee Stock Option \| Vesting in equal monthly installments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Monthly vesting installments	36 months

Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period, Number of Monthly Installments

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- Definition

Aggregate number of common shares reserved for future issuance.

+ 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

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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=6415400&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

Percentage of vesting of share-based compensation awards.

+ References

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