SUBSEQUENT EVENT (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 17, 2019
Subsequent Event [Line Items]
Proceeds from Issuance Initial Public Offering		$ 130,663	$ 153,530	$ 0
Common Stock | Subsequent Event
Subsequent Event [Line Items]
Issuance of common stock, net of costs (in shares)	1,854,838
Public offering stock price (USD per share)					$ 62.00
Proceeds from Issuance Initial Public Offering	$ 107,900