Stock Based Compensation - Restricted Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Unrecognized compensation cost related to unvested stock options	$ 12.3
Stock based compensation expense	6.2	$ 3.6
RSU
Unrecognized compensation cost related to unvested stock options	$ 3.2
Vesting period	3 years 1 month 6 days
Stock based compensation expense	$ 1.1	$ 0.2
Number of Shares
Beginning Balance	51
Granted (in shares)	123	51
Settled (in shares)	(25)
Forfeited (in shares)	(15)
Ending balance	133	51
Weighted Average Grant Date Fair Value
Beginning Balance	$ 33.16
Granted (per share)	27.61	33.16
Settled (per share)	30.43
Forfeited (per share)	30.58
Ending balance	$ 28.85	$ 33.16

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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