Share-based Compensation - RSU Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Earned Restricted Stock Units
Number of Shares
Non-vested RSUs, beginning balance (in shares)	1,075,359
Granted (in shares)	408,336
Vested (in shares)	(1,035,982)
Forfeited (in shares)	(3,282)
Non-vested RSUs, ending balance (in shares)	444,431
Weighted Average Grant Date Fair Value
Non-vested RSUs, beginning balance (in dollars per share)	$ 25.41
Granted (in dollars per share)	29.17
Vested (in dollars per share)	24.65
Forfeited (in dollars per share)	29.19
Non-vested RSUs, ending balance (in dollars per share)	$ 30.61
Unrecognized compensation expense	$ 12.2
Weighted-average period for recognition of compensation cost	2 years 25 days
Market Based Restricted Stock Units
Number of Shares
Granted (in shares)	58,007	187,809	108,424
Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 38.79	$ 30.48	$ 49.06
Performance Restricted Stock Units
Number of Shares
Granted (in shares)	58,013	204,374	108,498
Weighted Average Grant Date Fair Value
Granted (in dollars per share)	$ 38.79	$ 23.45	$ 33.68

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

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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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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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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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

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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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