Stock-Based Compensation Plans (Summary of Activity Related to Share Based Awards) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) $ / shares shares
Restricted Stock Units (RSUs) [Member]
Number of Shares
Nonvested, beginning \| shares	17,477
Granted \| shares	19,695
Vested \| shares	(3,455)
Forfeited \| shares	(3,492)
Nonvested, ending \| shares	30,225
Weighted Average Grant Date Fair Value
Nonvested, beginning \| $ / shares	$ 43.04
Granted \| $ / shares	45.06
Vested \| $ / shares	43.04
Forfeited \| $ / shares	44.13
Nonvested, ending \| $ / shares	$ 44.23
Weighted-Average Remaining Contractual Term (Years)
Nonvested, weighted average remaining contractual term	3 years 7 months 30 days
Aggregate Intrinsic Value
Nonvested, aggregate intrinsic value \| $	$ 1,087
Unrecognized Compensation
Nonvested, unrecognized compensation \| $	$ 1,090
Restricted Stock [Member]
Number of Shares
Nonvested, beginning \| shares	36,325
Granted \| shares	17,033
Vested \| shares	(26,527)
Forfeited \| shares	(4,050)
Nonvested, ending \| shares	22,781
Weighted Average Grant Date Fair Value
Nonvested, beginning \| $ / shares	$ 32.56
Granted \| $ / shares	44.19
Vested \| $ / shares	35.11
Forfeited \| $ / shares	32.96
Nonvested, ending \| $ / shares	$ 38.21
Weighted-Average Remaining Contractual Term (Years)
Nonvested, weighted average remaining contractual term	1 year 9 months
Aggregate Intrinsic Value
Nonvested, aggregate intrinsic value \| $	$ 819
Unrecognized Compensation
Nonvested, unrecognized compensation \| $	$ 531
Management Stock Purchase Plan [Member]
Number of Shares
Nonvested, beginning \| shares	20,219
Granted \| shares	9,372
Vested \| shares	(15,207)
Forfeited \| shares	(1,371)
Nonvested, ending \| shares	13,013
Weighted Average Grant Date Fair Value
Nonvested, beginning \| $ / shares	$ 9.77
Granted \| $ / shares	14.85
Vested \| $ / shares	8.56
Forfeited \| $ / shares	14.34
Nonvested, ending \| $ / shares	$ 14.35
Weighted-Average Remaining Contractual Term (Years)
Nonvested, weighted average remaining contractual term	9 months
Aggregate Intrinsic Value
Nonvested, aggregate intrinsic value \| $	$ 84
Unrecognized Compensation
Nonvested, unrecognized compensation \| $	$ 71
Performance Shares [Member]
Number of Shares
Nonvested, beginning \| shares	31,623
Granted \| shares	14,886
Vested \| shares	(9,844)
Forfeited \| shares	(10,288)
Nonvested, ending \| shares	26,377
Weighted Average Grant Date Fair Value
Nonvested, beginning \| $ / shares	$ 35.60
Granted \| $ / shares	44.56
Vested \| $ / shares	28.87
Forfeited \| $ / shares	32.75
Nonvested, ending \| $ / shares	$ 44.28
Weighted-Average Remaining Contractual Term (Years)
Nonvested, weighted average remaining contractual term	1 year 8 months 12 days
Aggregate Intrinsic Value
Nonvested, aggregate intrinsic value \| $	$ 949
Unrecognized Compensation
Nonvested, unrecognized compensation \| $	$ 314
DCRP Awards [Member]
Number of Shares
Nonvested, beginning \| shares	10,048
Granted \| shares	3,434
Vested \| shares	(2,899)
Forfeited \| shares	(613)
Nonvested, ending \| shares	9,970
Weighted Average Grant Date Fair Value
Nonvested, beginning \| $ / shares	$ 25.52
Granted \| $ / shares	45.23
Vested \| $ / shares	36.46
Forfeited \| $ / shares	41.56
Nonvested, ending \| $ / shares	$ 28.16
Weighted-Average Remaining Contractual Term (Years)
Nonvested, weighted average remaining contractual term	10 years 10 months 12 days
Aggregate Intrinsic Value
Nonvested, aggregate intrinsic value \| $	$ 359
Unrecognized Compensation
Nonvested, unrecognized compensation \| $	$ 251

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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-Publisher FASB
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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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-Publisher FASB
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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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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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