Stock-Based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	May 21, 2019
Stock-based Compensation Arrangement by Stock-based Payment Award [Line Items]
Number of shares authorized (in shares)			4,236,959
Shares available for issuance (in shares)	2,792,616
Stock-based compensation cost	$ 2.4	$ 2.0
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 17.5
Compensation cost not yet recognized, period for recognition	2 years
Performance-Based Restricted Stock Units
Stock-based Compensation Arrangement by Stock-based Payment Award [Line Items]
Granted, number of shares (in shares)	149,524	140,536
Grants in period, weighted average grant date fair value (in dollars per share)	$ 30.67	$ 25.32
Shares earned (in shares)		126,482
2010 LTIP \| Restricted Stock Units
Stock-based Compensation Arrangement by Stock-based Payment Award [Line Items]
Granted, number of shares (in shares)	225,724	271,107
Grants in period, weighted average grant date fair value (in dollars per share)	$ 30.68	$ 25.32

Share-Based Compensation Arrangement By Share-Based Payment Award, Non-Option Equity Instruments Earned

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

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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 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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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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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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