STOCK-BASED COMPENSATION - Summary of Option Activity (Details) - Options - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020
Stock Awards Plans
Stock options activity
Outstanding at the beginning of the period (in shares)	3,998,047
Granted (in shares)	0
Exercised (in shares)	(816,058)
Forfeited or expired (in shares)	(10,153)
Outstanding at the end of the period (in shares)	3,171,836
Stock option weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 70.28
Options granted, Weighted average exercise price per share (in dollars per share)	0
Options exercised, Weighted average exercise price per share (in dollars per share)	64.74
Options forfeited or expired, Weighted average exercise price per share (in dollars per share)	75.46
Outstanding at the end of the period (in dollars per share)	$ 71.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options exercisable, Number of options (in shares)	3,171,836
Options exercisable, Weighted average exercise price per share (in dollars per share)	$ 71.69
Options outstanding, Weighted average remaining contractual term (in years)	4 years 6 months
Options exercisable, Weighted average remaining contractual term (in years)	4 years 6 months
Options outstanding, Aggregate intrinsic value (in USD)	$ 221,908
Options exercisable, Aggregate intrinsic value (in USD)	221,908
Options exercised, Intrinsic value, at end of period	$ 63,407	$ 26,027
Director Stock Option Plans
Stock options activity
Outstanding at the beginning of the period (in shares)	99,200
Granted (in shares)	0
Exercised (in shares)	(47,500)
Forfeited or expired (in shares)	0
Outstanding at the end of the period (in shares)	51,700
Stock option weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 60.80
Options granted, Weighted average exercise price per share (in dollars per share)	0
Options exercised, Weighted average exercise price per share (in dollars per share)	57.40
Options forfeited or expired, Weighted average exercise price per share (in dollars per share)	0
Outstanding at the end of the period (in dollars per share)	$ 63.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options exercisable, Number of options (in shares)	51,700
Options exercisable, Weighted average exercise price per share (in dollars per share)	$ 63.91
Options outstanding, Weighted average remaining contractual term (in years)	2 years 7 months 6 days
Options exercisable, Weighted average remaining contractual term (in years)	2 years 7 months 6 days
Options outstanding, Aggregate intrinsic value (in USD)	$ 4,019
Options exercisable, Aggregate intrinsic value (in USD)	4,019
Options exercised, Intrinsic value, at end of period	$ 4,248	$ 1,973

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Weighted average price of options that were either forfeited or expired.

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Gross 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 remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, 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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