STOCK-BASED COMPENSATION PLAN Nonvested Restricted Stock Awards and Fair Value Assumptions (Details) - $ / shares	9 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 31.50	$ 29.57
Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	408,730	411,809
Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	30,961	26,416
2017 - TSR \| Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	40,819
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 32.17
Expected Volatility	20.80%
Risk-Free Interest Rate	1.47%
2017 - CEGR, Time \| Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	54,135
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 33.69
2018 - TSR \| Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	50,991
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 31.05
Expected Volatility	21.90%
Risk-Free Interest Rate	2.00%
2018 - CEGR, Time \| Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	83,989
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 31.23
2019 - TSR \| Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	38,934
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 32.88
Expected Volatility	23.20%
Risk-Free Interest Rate	2.40%
2019 - CEGR, Time \| Officers & Key Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	139,863
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 31.38
2019 \| Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding (in shares)	30,961
Weighted average fair value nonvested shares - ending balance (in dollars per share)	$ 27.07

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

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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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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-Publisher FASB
-Name Accounting Standards Codification
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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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