BUSINESS SEGMENTS - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	$ 211,784	$ 208,056	$ 648,913	$ 588,084
Operating income (loss)	35,675	37,567	123,385	114,957
Assets	5,590,341	5,010,812	5,590,341	5,010,812	$ 5,208,279
Goodwill	151,345		151,345		$ 90,544
Electricity
Segment Reporting Information [Line Items]
Goodwill	146,700	85,600	146,700	85,600
Electricity | Accounted for Under ASC 606
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	33,900	27,300	116,200	90,200
Product
Segment Reporting Information [Line Items]
Goodwill	0	0	0	0
Energy Storage and Management Services
Segment Reporting Information [Line Items]
Goodwill	4,600	4,600	4,600	4,600
Energy Storage and Management Services | Accounted for Under ASC 606
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	700	0	2,100	0
UNITED STATES
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	129,905	121,874	412,895	365,082
Non-US
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	81,879	86,182	236,018	223,002
Operating Segments | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	164,638	157,212	522,117	482,846
Operating income (loss)	30,977	34,787	119,072	120,457
Assets	5,001,907	4,481,600	5,001,907	4,481,600
Operating Segments | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	37,357	39,831	100,018	83,331
Operating income (loss)	3,034	2,374	4,902	(1,429)
Assets	189,824	190,157	189,824	190,157
Operating Segments | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	9,789	11,013	26,778	21,907
Operating income (loss)	1,664	406	(589)	(4,071)
Assets	398,610	339,055	398,610	339,055
Operating Segments | UNITED STATES | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	116,914	108,762	380,424	337,382
Operating Segments | UNITED STATES | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	3,202	2,099	5,693	5,793
Operating Segments | UNITED STATES | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	9,789	11,013	26,778	21,907
Operating Segments | Non-US | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	47,724	48,450	141,693	145,464
Operating Segments | Non-US | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	34,155	37,732	94,325	77,538
Operating Segments | Non-US | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	0	0	0	0
Segment Reconciling Items
Segment Reporting Information [Line Items]
Assets	126,767	128,218	126,767	128,218
Segment Reconciling Items | Electricity
Segment Reporting Information [Line Items]
Assets	126,767	128,218	126,767	128,218
Segment Reconciling Items | Product
Segment Reporting Information [Line Items]
Assets	0	0	0	0
Segment Reconciling Items | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Assets	0	0	0	0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	26,273	6,747	73,777	27,437
Intersegment Eliminations | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	0	0	0	0
Intersegment Eliminations | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	(26,273)	(6,747)	(73,777)	(27,437)
Intersegment Eliminations | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	$ 0	$ 0	$ 0	$ 0