SUPPLEMENTAL BALANCE SHEET INFORMATION - Deferred Charges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred charges
Initial franchise fees	$ 6,894	$ 5,101
Less - accumulated amortization	(1,673)	(1,374)
Total	5,221	3,727
Amortization expense	$ 400	$ 300	$ 400