Condensed Consolidated Statements of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues:
Revenues	$ 170,499,000	$ 166,480,000	$ 553,602,000	$ 528,802,000
Cost of revenues:
Cost of revenues	115,004,000	117,688,000	358,781,000	349,176,000
Gross profit	55,495,000	48,792,000	194,821,000	179,626,000
Operating expenses:
Research and development expenses	1,062,000	706,000	2,772,000	3,065,000
Selling and marketing expenses	3,783,000	8,578,000	10,924,000	15,989,000
General and administrative expenses	11,931,000	13,606,000	41,801,000	43,325,000
Write-off of unsuccessful exploration activities	0	0	0	119,000
Operating income	38,719,000	25,902,000	139,324,000	117,128,000
Other income (expense):
Interest income	482,000	214,000	1,195,000	516,000
Interest expense, net	(20,076,000)	(18,700,000)	(62,816,000)	(48,890,000)
Derivatives and foreign currency transaction gains (losses)	205,000	(383,000)	696,000	(2,511,000)
Income attributable to sale of tax benefits	4,056,000	4,066,000	16,457,000	14,983,000
Other non-operating income (expense), net	244,000	309,000	1,362,000	7,662,000
Income from operations before income tax and equity in earnings (losses) of investees	23,630,000	11,408,000	96,218,000	88,888,000
Income tax (provision) benefit	(9,626,000)	(1,184,000)	(20,136,000)	(3,347,000)
Equity in earnings (losses) of investees, net	1,085,000	(117,000)	3,334,000	1,481,000
Net income	15,089,000	10,107,000	79,416,000	87,022,000
Net income attributable to noncontrolling interest	516,000	474,000	(3,927,000)	(7,276,000)
Net income attributable to the Company's stockholders	15,605,000	10,581,000	75,489,000	79,746,000
Comprehensive income:
Net income	15,089,000	10,107,000	79,416,000	87,022,000
Other comprehensive income (loss), net of related taxes:
Change in foreign currency translation adjustments	(2,191,000)	(91,000)	(3,057,000)	(1,059,000)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment	(1,467,000)	1,012,000	(4,699,000)	4,175,000
Loss in respect of derivative instruments designated for cash flow hedge	18,000	20,000	58,000	60,000
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge	(7,000)	(14,000)	(24,000)	(44,000)
Comprehensive income	11,442,000	11,034,000	71,694,000	90,154,000
Comprehensive income attributable to noncontrolling interest	1,051,000	458,000	(3,254,000)	(7,088,000)
Comprehensive income attributable to the Company's stockholders	$ 12,493,000	$ 11,492,000	$ 68,440,000	$ 83,066,000
Basic:
Net income (in dollars per share)	$ 0.31	$ 0.21	$ 1.49	$ 1.58
Diluted:
Net income (in dollars per share)	$ 0.30	$ 0.21	$ 1.48	$ 1.56
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in shares)	50,933	50,645	50,816	50,627
Diluted (in shares)	51,334	50,963	51,124	50,985
Electricity [Member]
Revenues:
Revenue	$ 123,978,000	$ 116,891,000	$ 395,965,000	$ 371,559,000
Cost of revenues:
Cost of revenues	80,124,000	79,845,000	231,442,000	234,563,000
Product [Member]
Revenues:
Revenue	43,037,000	48,439,000	147,195,000	152,026,000
Cost of revenues:
Cost of revenues	31,073,000	35,669,000	114,495,000	106,968,000
Other Revenue [Member]
Revenues:
Revenue	3,484,000	1,150,000	10,442,000	5,217,000
Cost of revenues:
Cost of revenues	$ 3,807,000	$ 2,174,000	$ 12,844,000	$ 7,645,000