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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

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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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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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Share-Based Payments - Narrative (Details)	3 Months Ended	9 Months Ended
Share-Based Payments - Narrative (Details)	Sep. 30, 2018 USD ($) program	Sep. 30, 2018 USD ($) program	Sep. 30, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
General vesting period		3 years
Number of incentive programs \| program	3	3
Total unrecognized compensation cost related to unvested share-based payments	$ 115,400,000	$ 115,400,000
Weighted-average period for unrecognized compensation cost expected to be recognized		2 years 4 months 15 days
Proceeds from exercise of stock options		$ 0	$ 1,768,000
Stock Options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of stock option expiration from date of grant		10 years
Performance Cycle 2018-2020 \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	600,000	$ 600,000
Performance Cycle 2017-2019 \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation		500,000.0
Performance Cycle 2017-2019 \| Performance Shares Market Related Component
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	0	0
Performance Cycle 2016-2018 \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	0	0
Performance Cycle 2016-2018 \| Performance Shares Market Related Component
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 0	$ 0