Condensed Consolidated Statements of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Electricity	$ 109,795,000	$ 97,245,000	$ 321,664,000	$ 278,124,000
Product	74,822,000	65,607,000	174,408,000	145,446,000
Total revenues	184,617,000	162,852,000	496,072,000	423,570,000
Cost of revenues:
Electricity	66,481,000	61,501,000	192,410,000	179,604,000
Product	43,647,000	42,019,000	99,504,000	89,826,000
Total cost of revenues	110,128,000	103,520,000	291,914,000	269,430,000
Gross margin	74,489,000	59,332,000	204,158,000	154,140,000
Operating expenses:
Research and development expenses	1,086,000	335,000	2,030,000	1,112,000
Selling and marketing expenses	4,793,000	4,383,000	12,136,000	12,099,000
General and administrative expenses	19,093,000	7,950,000	36,625,000	25,597,000
Write-off of unsuccessful exploration activities	1,294,000	185,000	2,714,000	359,000
Operating income	48,223,000	46,479,000	150,653,000	114,973,000
Other income (expense):
Interest income	266,000	53,000	831,000	106,000
Interest expense, net	(17,137,000)	(17,748,000)	(51,561,000)	(54,435,000)
Derivatives and foreign currency transaction gains (losses)	(222,000)	1,296,000	(2,592,000)	(641,000)
Income attributable to sale of tax benefits	3,463,000	8,634,000	12,380,000	18,917,000
Other non-operating income (expense), net	(5,546,000)	(131,000)	(5,306,000)	(1,523,000)
Income from continuing operations before income taxes and equity in losses of investees	29,047,000	38,583,000	104,405,000	77,397,000
Income tax (provision) benefit	(11,988,000)	38,211,000	(29,387,000)	26,696,000
Equity in losses of investees, net	(2,653,000)	(3,133,000)	(4,734,000)	(4,892,000)
Income from continuing operations	14,406,000	73,661,000	70,284,000	99,201,000
Net income attributable to noncontrolling interest	(2,326,000)	(1,522,000)	(4,584,000)	(2,616,000)
Net income attributable to the Company's stockholders	12,080,000	72,139,000	65,700,000	96,585,000
Comprehensive income:
Net income	14,406,000	73,661,000	70,284,000	99,201,000
Other comprehensive income (loss), net of related taxes:
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment	1,337,000	(4,318,000)	(3,829,000)	(4,154,000)
Loss in respect of derivative instruments designated for cash flow hedge	22,000	22,000	65,000	68,000
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge	(24,000)	(29,000)	(72,000)	(90,000)
Comprehensive income	15,741,000	69,336,000	66,448,000	95,025,000
Comprehensive income attributable to noncontrolling interest	(2,326,000)	(1,522,000)	(4,584,000)	(2,616,000)
Comprehensive income attributable to the Company's stockholders	$ 13,415,000	$ 67,814,000	$ 61,864,000	$ 92,409,000
Earnings per share attributable to the Company's stockholders:
Net income (in dollars per share)	$ 0.24	$ 1.47	$ 1.33	$ 2
Net income (in dollars per share)	$ 0.24	$ 1.41	$ 1.31	$ 1.93
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in shares)	49,599	49,023	49,410	48,388
Diluted (in shares)	50,289	51,113	50,097	50,011
Common Stock, Dividends, Per Share, Declared	$ 0.07	$ 0.06	$ 0.45	$ 0.20