Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents 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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Stock-Based Compensation - Performance Share Units (Details) - Performance share units - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining recognition period of unrecognized stock-based compensation costs		2 years 2 months 12 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs related to unvested options (up to)	$ 16.3	$ 16.3
Long-term incentive plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeited (in shares)		7,940	5,719
Executive Management
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Executive Management \| Long-term incentive plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock unit granted to an executive (in shares)		125,232	99,718
Vested (in shares)	0	0	11,037