STOCK-BASED COMPENSATION - Other Information (Details) - Restricted Stock - USD ($)	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation
Fair value, shares vested	$ 6,970,000	$ 16,194,000
Tax (expense) benefits for compensation tax deductions in excess of compensation expense	(510,000)	$ 1,620,000
Unrecognized compensation cost related to non-vested restricted shares	$ 48,384,000
Unrecognized compensation cost related to non-vested restricted shares recognized period	3 years 10 months 24 days

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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