INCOME TAXES- Deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Outside basis difference in SES Holdings	$ 37,931	$ 3,601
Net operating losses	35,243	3,999
Credits and other carryforwards	863	297
Property and equipment		362
Intangible assets	1,218
Stock compensation	2,557
Other	1,340
Total deferred tax assets before valuation allowance	79,152	8,259
Valuation allowance	(75,886)	(7,932)
Total deferred tax assets	3,266	327
Deferred tax liabilities
Property and equipment	3,286
Intangible assets		811
Other	549	113
Total deferred tax liabilities	3,835	924
Net deferred tax (liabilities)	$ (569)	$ (597)