STOCKHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2018
Equity [Line Items]
Stock repurchased and retired (in shares)	1,261,828	1,261,828	820,328
Repurchase Plan 2020 | Common Stock
Equity [Line Items]
Number of shares authorized to be repurchased (in shares)				2,350,000
Repurchase Plan 2018
Equity [Line Items]
Common stock repurchased, average price (in dollars per share)		$ 43.05
Stock repurchased and retired		$ 54.3
Repurchase Plan 2018 | Common Stock
Equity [Line Items]
Stock repurchased (in shares)		1,261,828
Common stock repurchased, average price (in dollars per share)				$ 33.58
Stock repurchased and retired			$ 25.7	$ 50.0
Shares available for issuance (in shares)					1,800,000
Stock repurchased and retired (in shares)			820,328	1,488,519