SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Effect of Adoption of ASU 2014-09 (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 321,508	$ 357,358	$ 343,896	$ 303,443	$ 278,992	$ 303,116	$ 294,822	$ 255,311	$ 1,326,205	$ 1,132,241	$ 736,386
Operating costs and expenses by segment:									1,287,560	1,068,335	884,257
Operating income (loss) by segment:	6,157	24,726	11,403	(3,641)	17,885	33,515	23,262	(10,756)	38,645	63,906	(147,871)
Net earnings	$ (95)	$ 18,324	$ 7,234	$ 9,851	$ 36,812	$ 26,786	$ 23,023	$ (9,114)
Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Revenue										1,132,241
Operating costs and expenses by segment:										1,068,335
Operating income (loss) by segment:										63,906
Net earnings										77,507
Accounting Standards Update 2014-09 | Under ASC 605
Disaggregation of Revenue [Line Items]
Revenue										1,132,241
Operating costs and expenses by segment:										1,073,275
Operating income (loss) by segment:										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 by segment:										(4,940)
Operating income (loss) by segment:										4,940
Net earnings										3,715
North America
Disaggregation of Revenue [Line Items]
Revenue									1,249,892	1,062,171	678,897
Operating income (loss) by segment:									48,967	78,102	(128,483)
North America | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Revenue										1,062,171
Operating costs and expenses by segment:										984,069
Operating income (loss) by segment:										78,102
North America | Accounting Standards Update 2014-09 | Under ASC 605
Disaggregation of Revenue [Line Items]
Revenue										1,062,171
Operating costs and expenses by segment:										989,004
Operating income (loss) by segment:										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 by segment:										(4,935)
Operating income (loss) by segment:										4,935
Europe
Disaggregation of Revenue [Line Items]
Revenue									76,313	70,070	57,489
Operating income (loss) by segment:									$ (10,322)	(14,196)	$ (19,388)
Europe | Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Revenue										70,070
Operating costs and expenses by segment:										84,266
Operating income (loss) by segment:										(14,196)
Europe | Accounting Standards Update 2014-09 | Under ASC 605
Disaggregation of Revenue [Line Items]
Revenue										70,070
Operating costs and expenses by segment:										84,271
Operating income (loss) by segment:										(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 by segment:										(5)
Operating income (loss) by segment:										$ 5