OTHER CURRENT ASSETS AND OTHER ASSETS - Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
OTHER CURRENT ASSETS AND OTHER ASSETS
Non-trade receivables	$ 6,379	$ 7,668
Prepaid rent	4,442	4,248
Prepaid maintenance	2,896	3,134
Restricted cash	2,349	3,271	$ 2,243	$ 2,255
Prepaid other	1,160	1,436
Prepaid insurance	1,627	271
Other	1,151	860
Total other current assets	$ 20,004	$ 20,888