Stock-based Compensation - Additional Information (Details) shares in Thousands	6 Months Ended
Jun. 30, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market condition period	3 years
Performance measurement period	3 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period range (in percent)	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period range (in percent)	200.00%
Restricted Stock Awards, Including Three Year Market Condition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted (in shares)	207

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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.

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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

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- Definition

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

+ References

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- Definition

Percentage of vesting of share-based compensation awards.

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