Share-Based Compensation - Activity in stock plan (Details) - 2009 Plan - Restricted stock awards - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Restricted Stock Awards
Outstanding at beginning of period	337,014	336,397
Granted	70,617	76,031
Vested	(53,882)	(76,753)
Forfeited or cancelled	(6,138)
Outstanding at end of period	347,611	335,675
Weighted Average Grant Date Fair Value
Outstanding at beginning of period	$ 18.36	$ 15.38
Granted	19.87	22.67
Vested	18.69	10.56
Forfeited or cancelled	17.34
Outstanding at end of period	$ 18.64	$ 18.13
Additional disclosures
Unrecognized compensation cost	$ 3.6
Weighted average period	3 years 3 months 15 days

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 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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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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 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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