Stock Based Compensation - Stock Options, Restricted Stock Units and Performance Units Narrative (Details) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares
Options to purchase common stock
Stock-based Compensation
Weighted-average grant-date fair value (in dollars per share) \| $ / shares	$ 14.35	$ 12.87
Total unrecognized compensation expense	$ 30.0	$ 30.0
Weighted average period over which unrecognized compensation is expected to be recognized		2 years 6 months
RSUs
Stock-based Compensation
Total unrecognized compensation expense	$ 12.1	$ 12.1
Weighted average period over which unrecognized compensation is expected to be recognized		2 years 8 months 26 days
PSUs
Stock-based Compensation
Number of shares authorized (in shares) \| shares	79,000	79,000

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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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Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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