CONTRACT REVENUE AND PERCENTAGE-OF-COMPLETION METHOD - Revenues by Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Geographic Reporting Disclosure [Line Items]
Revenue	$ 37,277	$ 49,884	$ 45,868	$ 37,993	$ 55,461	$ 65,384	$ 81,502	$ 83,979	$ 171,022	$ 286,326	$ 306,120
United States
Geographic Reporting Disclosure [Line Items]
Revenue									171,022	245,039	287,892
International
Geographic Reporting Disclosure [Line Items]
Revenue									$ 0	$ 41,287	$ 18,228