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Stock Based Compensation - Stock Options, Restricted Stock Units and Performance Units Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Feb. 28, 2019
Options to purchase common stock
Stock-based Compensation
Weighted-average grant-date fair value (in dollars per share)	$ 14.26	$ 12.68
Total unrecognized compensation expense	$ 33.3	$ 33.3
Weighted average period over which unrecognized compensation is expected to be recognized		2 years 6 months 29 days
RSUs
Stock-based Compensation
Total unrecognized compensation expense	$ 14.0	$ 14.0
Weighted average period over which unrecognized compensation is expected to be recognized		2 years 11 months 8 days
PSUs
Stock-based Compensation
Number of shares authorized (in shares)			79,000