STOCK-BASED COMPENSATION - Employee Stock Purchase Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Stock Purchase Plan
Stock-based compensation	$ 20,230	$ 16,162	$ 17,318
Employee Stock Purchase Plan
Employee Stock Purchase Plan
Shares purchased (in shares)	92,738	90,084	49,247
Shares issued (in shares)	92,738	90,084	49,247
Discounted price (in dollars per share)	$ 12.64	$ 9.74	$ 11.08
Stock-based compensation	$ 234	$ 141	$ 154