STOCKHOLDERS' EQUITY - Unvested restricted stock outstanding (Details)	9 Months Ended
	Sep. 30, 2021 $ / shares shares
STOCKHOLDERS' EQUITY
Balance outstanding at the beginning of the period (in shares) | shares	2,870,000
Forteited (in shares) | shares	(56,000)
Vested (in shares) | shares	(851,000)
Granted (in shares) | shares	778,000
Balance outstanding at the end of the period (in shares) | shares	2,741,000
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 20.36
Forfeited (in dollars per share) | $ / shares	24.80
Vested (in dollars per share) | $ / shares	16.62
Granted (in dollars per share) | $ / shares	37.04
Balance at the end of the period (in dollars per share) | $ / shares	$ 26.16