Stock-based Compensation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stock-based Compensation
Recorded compensation costs for the RSAs and RSUs	$ 1.8	$ 1.4	$ 3.1	$ 5.3
RSAs
Stock-based Compensation
Granted (in shares)	0	0	39,915	36,183
Canceled (in shares)	2,153	2,739	9,338	14,394
Weighted average grant date fair value (in dollars per share)			$ 51.41	$ 52.83
RSUs
Stock-based Compensation
Granted (in shares)	0	0	32,720	26,473
Awards issued (in shares)	0	0	41,731	62,726
Canceled (in shares)	0	0	22,936	31,177
Weighted average grant date fair value (in dollars per share)			$ 51.41	$ 52.83
Performance period			3 years
Employees \| RSAs
Stock-based Compensation
Vesting period			36 months
Director \| RSAs
Stock-based Compensation
Vesting period			12 months

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

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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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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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