Share-Based Compensation Plan - Activity in stock (Details) - 2009 Plan - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Stock Awards and Units
Restricted Stock Awards and Units
Outstanding at beginning of period	347,211	337,014
Granted	82,494	70,617
Vested	(91,346)	(53,994)
Forfeited or cancelled	(13,329)	(6,426)
Outstanding at end of period	325,030	347,211	337,014
Weighted Average Grant Date Fair Value
Outstanding at beginning of period	$ 18.64	$ 18.36
Granted	19.62	19.87
Vested	16.39	18.76
Forfeited or cancelled	19.62	17.63
Outstanding at end of period	$ 19.48	$ 18.64	$ 18.36
Additional disclosures
Unrecognized compensation cost	$ 2.8	$ 3.3
Weighted average period	3 years 5 months 4 days	3 years 10 months 9 days
Compensation expense	$ 1.9	$ 1.5	$ 1.2
Restricted stock awards
Restricted Stock Awards and Units
Outstanding at beginning of period	262,734
Outstanding at end of period	203,253	262,734
Restricted stock units
Restricted Stock Awards and Units
Outstanding at beginning of period	84,477
Outstanding at end of period	73,236	84,477

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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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 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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