GOODWILL - Schedule of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 296,838	$ 307,952	$ 307,960	$ 312,689
Accumulated impairment losses, beginning of period	(108,400)	(108,400)	(108,400)	(1,663)
Goodwill, net, beginning of period	188,438	199,552	199,560	311,026
Goodwill impairments				(106,737)
Impact of divestiture on goodwill		(11,101)		(4,685)
Effects of foreign currency	5	(13)	(8)	(44)
Goodwill, end of period	296,843	296,838	307,952	307,960
Accumulated impairment losses	(108,400)	(108,400)	(108,400)	(108,400)
Goodwill, net, end of period	188,443	188,438	199,552	199,560
Transportation Solutions
Goodwill [Roll Forward]
Goodwill, beginning of period	188,762	188,770	188,775	193,488
Accumulated impairment losses, beginning of period	(68,257)	(68,257)	(68,257)	0
Goodwill, net, beginning of period	120,505	120,513	120,518	193,488
Goodwill impairments				(68,257)
Impact of divestiture on goodwill		0		(4,685)
Effects of foreign currency	3	(8)	(5)	(28)
Goodwill, end of period	188,765	188,762	188,770	188,775
Accumulated impairment losses	(68,257)	(68,257)	(68,257)	(68,257)
Goodwill, net, end of period	120,508	120,505	120,513	120,518
Parts & Service
Goodwill [Roll Forward]
Goodwill, beginning of period	108,076	119,182	119,185	119,201
Accumulated impairment losses, beginning of period	(40,143)	(40,143)	(40,143)	(1,663)
Goodwill, net, beginning of period	67,933	79,039	79,042	117,538
Goodwill impairments				(38,480)
Impact of divestiture on goodwill		(11,101)		0
Effects of foreign currency	2	(5)	(3)	(16)
Goodwill, end of period	108,078	108,076	119,182	119,185
Accumulated impairment losses	(40,143)	(40,143)	(40,143)	(40,143)
Goodwill, net, end of period	$ 67,935	$ 67,933	$ 79,039	$ 79,042