SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Change during the year (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Beginning of year	$ 158,572	$ 89,750	$ 19,960
Acquired goodwil	(1,628)
Acquired goodwill		68,822	69,790
End of year	$ 156,944	$ 158,572	$ 89,750