SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Effect of Adoption of ASU 2014-09 (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 278,992	$ 303,116	$ 294,822	$ 255,311	$ 223,213	$ 181,717	$ 180,711	$ 150,745	$ 1,132,241	$ 736,386	$ 498,890
Operating costs and Expenses									1,068,335	884,257	474,832
Operating income (loss)	17,885	33,515	23,262	(10,756)	(33,918)	(112,505)	(2,836)	1,388	63,906	(147,871)	24,058
Net earnings	$ 36,812	$ 26,786	$ 23,023	$ (9,114)	$ (58,231)	$ (72,158)	$ (25)	$ 25,887	77,507
Under ASC 605
Disaggregation of Revenue [Line Items]
Revenue									1,132,241
Operating costs and Expenses									1,073,275
Operating income (loss)									58,966
Net earnings									73,792
Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09
Disaggregation of Revenue [Line Items]
Revenue									0
Operating costs and Expenses									(4,940)
Operating income (loss)									4,940
Net earnings									3,715
North America
Disaggregation of Revenue [Line Items]
Revenue									1,062,171	678,897	461,847
Operating costs and Expenses									984,069
Operating income (loss)									78,102	(128,483)	32,464
North America | Under ASC 605
Disaggregation of Revenue [Line Items]
Revenue									1,062,171
Operating costs and Expenses									989,004
Operating income (loss)									73,167
North America | Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09
Disaggregation of Revenue [Line Items]
Revenue									0
Operating costs and Expenses									(4,935)
Operating income (loss)									4,935
Europe
Disaggregation of Revenue [Line Items]
Revenue									70,070	57,489	37,043
Operating costs and Expenses									84,266
Operating income (loss)									(14,196)	$ (19,388)	$ (8,406)
Europe | Under ASC 605
Disaggregation of Revenue [Line Items]
Revenue									70,070
Operating costs and Expenses									84,271
Operating income (loss)									(14,201)
Europe | Accounting Standards Update 2014-09 | Effect of adoption of ASU No. 2014-09
Disaggregation of Revenue [Line Items]
Revenue									0
Operating costs and Expenses									(5)
Operating income (loss)									$ 5