REVENUE FROM CONTRACTS FROM CUSTOMERS Revenue by Customer Type and Contract Type (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Revenue	$ 125,742
Department of Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	94,201
Department of Defense [Member] | Cost Reimbursement Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	42,828
Department of Defense [Member] | Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	26,145
Department of Defense [Member] | Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	25,228
Non-Department of Defense U.S. Government [Member]
Disaggregation of Revenue [Line Items]
Revenue	23,459
Non-Department of Defense U.S. Government [Member] | Cost Reimbursement Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,778
Non-Department of Defense U.S. Government [Member] | Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	18,900
Non-Department of Defense U.S. Government [Member] | Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,781
Commercial and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	8,082
Commercial and Other [Member] | Cost Reimbursement Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	0
Commercial and Other [Member] | Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,382
Commercial and Other [Member] | Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 6,700