Stock-Based Compensation - Restricted Stock and Restricted Share Awards (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation
Period for recognition of unrecognized compensation expense	1 year 1 month 6 days
Restricted Stock
Number of Shares
Unvested as of beginning of period (in shares)	139,718
Granted (in shares)	172,046	162,550	0
Vested (in shares)	(48,340)	(11,239)
Forfeited (in shares)	(1,047)	(11,593)
Unvested as of end of period (in shares)	262,377	139,718
Weighted Average Grant Date Fair Value
Unvested as of beginning of period (in dollars per share)	$ 27.04
Granted (in dollars per share)	25.96	$ 27.06
Vested (in dollars per share)	27.03	27.37
Forfeited (in dollars per share)	25.96	27.04
Unvested as of end of period (in dollars per share)	$ 26.35	$ 27.04
Stock-based compensation
Total fair value of vested shares (in dollars)	$ 1.3	$ 0.3
Unrecognized compensation expense	$ 4.1	$ 2.9

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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Amount of cost to be recognized for option under share-based payment arrangement.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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