Condensed Consolidated Statements of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Electricity	$ 104,001,000	$ 90,926,000	$ 211,869,000	$ 180,879,000
Product	55,860,000	49,561,000	99,586,000	79,839,000
Total revenues	159,861,000	140,487,000	311,455,000	260,718,000
Cost of revenues:
Electricity	62,243,000	62,522,000	125,929,000	118,103,000
Product	31,822,000	27,182,000	55,857,000	47,807,000
Total cost of revenues	94,065,000	89,704,000	181,786,000	165,910,000
Gross margin	65,796,000	50,783,000	129,669,000	94,808,000
Operating expenses:
Research and development expenses	595,000	414,000	944,000	777,000
Selling and marketing expenses	3,668,000	4,283,000	7,343,000	7,716,000
General and administrative expenses	8,783,000	7,443,000	17,532,000	17,647,000
Write-off of unsuccessful exploration activities	863,000	0	1,420,000	174,000
Operating income	51,887,000	38,643,000	102,430,000	68,494,000
Other income (expense):
Interest income	245,000	44,000	565,000	53,000
Interest expense, net	(18,401,000)	(18,859,000)	(34,424,000)	(36,687,000)
Derivatives and foreign currency transaction gains (losses)	(4,332,000)	(571,000)	(2,370,000)	(1,937,000)
Income attributable to sale of tax benefits	4,519,000	4,731,000	8,917,000	10,283,000
Other non-operating income (expense), net	49,000	(1,675,000)	240,000	(1,392,000)
Income from continuing operations before income taxes and equity in losses of investees	33,967,000	22,313,000	75,358,000	38,814,000
Income tax (provision) benefit	(7,890,000)	(6,056,000)	(17,399,000)	(11,515,000)
Equity in losses of investees, net	(1,144,000)	(984,000)	(2,081,000)	(1,759,000)
Income from continuing operations	24,933,000	15,273,000	55,878,000	25,540,000
Net income attributable to noncontrolling interest	(584,000)	(859,000)	(2,258,000)	(1,094,000)
Net income attributable to the Company's stockholders	24,349,000	14,414,000	53,620,000	24,446,000
Comprehensive income:
Net income	24,933,000	15,273,000	55,878,000	25,540,000
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	(1,987,000)	3,460,000	(5,166,000)	164,000
Loss in respect of derivative instruments designated for cash flow hedge	22,000	23,000	43,000	46,000
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge	(24,000)	(31,000)	(48,000)	(61,000)
Comprehensive income	22,944,000	18,725,000	50,707,000	25,689,000
Comprehensive income attributable to noncontrolling interest	(584,000)	(859,000)	(2,258,000)	(1,094,000)
Comprehensive income attributable to the Company's stockholders	$ 22,360,000	$ 17,866,000	$ 48,449,000	$ 24,595,000
Earnings per share attributable to the Company's stockholders:
Net income (in dollars per share)	$ 0.49	$ 0.29	$ 1.09	$ 0.51
Net income (in dollars per share)	$ 0.49	$ 0.28	$ 1.07	$ 0.49
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in shares)	49,456	48,881	49,314	48,063
Diluted (in shares)	50,137	50,600	49,977	49,444
Common Stock, Dividends, Per Share, Declared	$ 0.07	$ 0.06	$ 0.38	$ 0.12