Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Electricity	$ 436,292	$ 375,920	$ 382,301
Product	226,299	218,724	177,223
Total revenues	662,591	594,644	559,524
Cost of revenues:
Electricity	261,573	242,612	246,630
Product	130,223	133,753	109,143
Total cost of revenues	391,796	376,365	355,773
Gross profit	270,795	218,279	203,751
Operating expenses:
Research and development expenses	2,762	1,780	783
Selling and marketing expenses	16,424	16,077	15,425
General and administrative expenses	46,710	34,782	28,614
Write-off of unsuccessful exploration activities	3,017	1,579	15,439
Operating income	201,882	164,061	143,490
Other income (expense):
Interest income	971	297	312
Interest expense, net	(67,389)	(72,577)	(84,654)
Derivatives and foreign currency transaction gains (losses)	(5,534)	(1,622)	(5,839)
Income attributable to sale of tax benefits	16,503	25,431	24,143
Gain from sale of property, plant and equipment			7,628
Other non-operating income (expense), net	(5,345)	(1,991)	756
Income from continuing operations before income taxes and equity in losses of investees	141,088	113,599	85,836
Income tax (provision) benefit	(31,837)	15,258	(27,608)
Equity in losses of investees, net	(7,735)	(5,508)	(3,213)
Income from continuing operations	101,516	123,349	55,015
Net income attributable to noncontrolling interest	(7,586)	(3,776)	(833)
Net income attributable to the Company's stockholders	93,930	119,573	54,182
Comprehensive income:
Net income	101,516	123,349	55,015
Other comprehensive income (loss), net of related taxes:
Currency translation adjustments	(1,648)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment	1,185	1,028	(8,112)
Loss in respect of derivative instruments designated for cash flow hedge	87	91	(902)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge	(96)	(118)	(141)
Comprehensive income	101,044	124,350	45,860
Comprehensive income attributable to noncontrolling interest	(7,179)	(3,776)	(833)
Comprehensive income attributable to the Company's stockholders	$ 93,865	$ 120,574	$ 45,027
Basic:
Net income (in dollars per share)	$ 1.90	$ 2.46	$ 1.19
Diluted:
Net income (in dollars per share)	$ 1.87	$ 2.43	$ 1.18
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in shares)	49,469	48,562	45,508
Diluted (in shares)	50,140	49,187	45,859
Dividend per share declared (in dollars per share)	$ 0.52	$ 0.26	$ 0.21