STOCKHOLDERS' EQUITY - Stock Options (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, granted (in shares)	0	0	0
Options
Exercised (in shares)	(38,920)	(14,213)
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, granted (in shares)	0	0	0
Options
Outstanding at period start (in shares)	70,628	112,094	176,959	248,201
Forfeited or expired (in shares)	(2,546)	(50,652)	(71,242)
Outstanding at period end (in shares)	112,094	176,959	248,201
Weighted-Average Exercise Price
Outstanding at period start, weighted-average exercise price (in dollars per share)	$ 30.32	$ 29.42	$ 23.81
Forfeited or expired, weighted-average exercise price (in dollars per share)	27.61	27.61	9.85
Exercised (in dollars per share)	29.30	29.85
Outstanding at period end, weighted-average exercise price (in dollars per share)	$ 30.97	$ 30.32	$ 29.42	$ 23.81
Weighted-Average Remaining Contractual Terms (in Years)
Weighted-Average Remaining Contractual Terms (in Years)	1 year 2 months 12 days	1 year 9 months 18 days	2 years	2 years 4 months 24 days
Vesting period (in years)	3 years
Stock-based compensation expense	$ 0	$ 0	$ 0

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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