STOCKHOLDERS' EQUITY AND EQUITY INSTRUMENTS (Summary of Activity) (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Options
Stock option activity
Outstanding at beginning of period (in shares)	708,746	562,877	442,755
Granted (in shares)	369,716	250,514	227,351
Exercised (in shares)	0	0	(3,366)
Cancelled/Expired (in shares)	(190,595)	(104,645)	(103,863)
Outstanding at end of period (in shares)	887,867	708,746	562,877
Stock option weighted-average exercise price
Outstanding at beginning of period (in dollars per share)	$ 70.76	$ 75.89	$ 80.07
Granted (in dollars per share)	54.15	59.61	68.00
Exercised (in dollars per share)	0	0	76.03
Cancelled/Expired (in dollars per share)	69.06	71.65	76.44
Outstanding at end of period (in dollars per share)	$ 64.21	$ 70.76	$ 75.89
RSUs
RSU and PSU activity
Outstanding at beginning of period (in shares)	83,308	70,856	63,780
Granted (in shares)	218,071	42,013	34,635
Released from restriction (in shares)	(32,630)	(16,905)	(15,806)
Cancelled/Expired (in shares)	(51,336)	(12,656)	(11,753)
Outstanding at end of period (in shares)	217,413	83,308	70,856
RSU and PSU weighted-average fair value
Outstanding at beginning of period (in dollars per share)	$ 65.75	$ 74.63	$ 80.25
Granted (in dollars per share)	49.73	60.28	68.00
Released from restriction (in dollars per share)	66.95	88.78	84.77
Cancelled/Expired (in dollars per share)	54.87	66.53	71.96
Outstanding at end of period (in dollars per share)	$ 52.07	$ 65.75	$ 74.63
PSUs
RSU and PSU activity
Outstanding at beginning of period (in shares)	126,638	112,036	89,011
Granted (in shares)	123,003	67,235	58,878
Released from restriction (in shares)		(2,753)	(12,946)
Cancelled/Expired (in shares)	(70,244)	(49,880)	(22,907)
Outstanding at end of period (in shares)	179,397	126,638	112,036
RSU and PSU weighted-average fair value
Outstanding at beginning of period (in dollars per share)	$ 69.06	$ 79.48	$ 89.43
Granted (in dollars per share)	56.88	64.30	73.08
Released from restriction (in dollars per share)		78.92	105.77
Cancelled/Expired (in dollars per share)	67.20	85.51	86.81
Outstanding at end of period (in dollars per share)	$ 61.43	$ 69.06	$ 79.48

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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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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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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Net number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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

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