BUSINESS SEGMENTS - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	$ 212,963	$ 194,796	$ 437,129	$ 380,028
Operating income (loss)	35,127	24,224	87,710	77,390
Assets	5,506,802	5,010,644	5,506,802	5,010,644	$ 5,208,279
Goodwill	151,074		151,074		$ 90,544
Electricity
Segment Reporting Information [Line Items]
Goodwill	146,400	85,800	146,400	85,800
Electricity | Accounted for Under ASC 606
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	37,500	30,200	82,300	62,900
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	1,400	0
UNITED STATES
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	130,218	114,476	282,991	243,208
Non-US
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	82,745	80,320	154,138	136,820
Operating Segments | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	166,226	155,324	357,479	325,634
Operating income (loss)	35,414	28,661	88,095	85,669
Assets	4,955,806	4,576,437	4,955,806	4,576,437
Operating Segments | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	37,829	33,458	62,661	43,500
Operating income (loss)	1,026	(2,297)	1,868	(3,802)
Assets	192,092	182,437	192,092	182,437
Operating Segments | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	8,908	6,014	16,989	10,894
Operating income (loss)	(1,313)	(2,140)	(2,253)	(4,477)
Assets	358,904	251,770	358,904	251,770
Operating Segments | UNITED STATES | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	119,695	106,209	263,511	228,620
Operating Segments | UNITED STATES | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	1,615	2,253	2,491	3,694
Operating Segments | UNITED STATES | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	8,908	6,014	16,989	10,894
Operating Segments | Non-US | Electricity
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	46,531	49,115	93,968	97,014
Operating Segments | Non-US | Product
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	36,214	31,205	60,170	39,806
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	129,664	126,451	129,664	126,451
Segment Reconciling Items | Electricity
Segment Reporting Information [Line Items]
Assets	129,664	126,451	129,664	126,451
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	26,907	12,918	47,504	20,690
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	(26,907)	(12,918)	(47,504)	(20,690)
Intersegment Eliminations | Energy Storage and Management Services
Segment Reporting Information [Line Items]
Revenue from contract with customer, including assessed tax	$ 0	$ 0	$ 0	$ 0