INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Income Tax Assets
Accrued liabilities	$ 1,264	$ 334
Allowance for doubtful accounts	94	195
Goodwill and other intangible assets	5,304	10,953
Stock‑based compensation	2,960	1,692
Net operating losses	56,788	49,267
Other	69	389
Noncurrent deferred tax assets	66,479	62,830
Total deferred tax assets	66,479	62,830
Valuation allowance	(1,151)	(879)
Total deferred tax assets — net	65,328	61,951
Deferred Income Tax Liabilities
Property and equipment	(68,811)	(60,958)
Prepaid expenses	(965)	(1,506)
Other	(131)	(635)
Noncurrent deferred tax liabilities	(69,907)	(63,099)
Net deferred tax liability	$ (4,579)	$ (1,148)