SUBSEQUENT EVENTS (Details) - USD ($) $ in Thousands		1 Months Ended		9 Months Ended
	Nov. 08, 2017	Apr. 30, 2017	Apr. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Apr. 02, 2015
Subsequent events
Payment of a prepayment fee				$ 4,000	$ 5,000
Senior Notes
Subsequent events
Amount of debt prepaid		$ 100,000	$ 100,000
Aggregate principal amount of notes issued			375,000	$ 375,000		$ 575,000
Payment of a prepayment fee		$ 4,000	$ 5,000
Subsequent events | Senior Notes
Subsequent events
Amount of debt prepaid	$ 10,000
Payment of a prepayment fee	$ 400