Share-Based Compensation - Plans (Details)	9 Months Ended
Sep. 30, 2018 shares
Share-Based Compensation
Options granted, net of cancellation	234,959
Earned Restricted Stock Units
Share-Based Compensation
Stock incentive plan, vesting period	4 years
Market Based Restricted Stock Units [Member]
Share-Based Compensation
Stock incentive plan, vesting period	24 months
Vesting Two Years From January 31 of Grant Year \| Restricted Stock Units
Share-Based Compensation
Stock incentive plan, vesting period	24 months
Vesting percentage	50.00%
Vesting Three Years From January 31 of Grant Year \| Restricted Stock Units
Share-Based Compensation
Stock incentive plan, vesting period	36 months
Vesting percentage	25.00%
Vesting Four Years From January 31 of Grant Year \| Restricted Stock Units
Share-Based Compensation
Stock incentive plan, vesting period	48 months
Vesting percentage	25.00%

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.

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)
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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.

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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