PROPERTY AND EQUIPMENT - Summary of Depreciation and Amortization of Property and Equipment (Details) - USD ($)	3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Costs of sales and services						$ 75,998,000	$ 70,368,000	$ 71,626,000
Other depreciation and amortization						10,644,000	2,478,000	2,274,000
Subtotal						86,642,000	72,846,000	73,900,000
Amortization of acquired and developed technologies						4,034,000	2,147,000	3,048,000
Total depreciation and amortization	$ 23,309,000	$ 22,468,000	$ 20,996,000	$ 43,464,000	$ 66,771,000	$ 90,676,000	$ 74,993,000	$ 76,948,000