Consolidated Statements of Operations and Comprehensive Income (Loss) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Electricity	$ 382,301	$ 329,747	$ 314,894
Product	177,223	203,492	186,879
Total revenues	559,524	533,239	501,773
Cost of revenues:
Electricity	246,630	232,874	237,415
Product	109,143	140,547	135,346
Total cost of revenues	355,773	373,421	372,761
Gross margin	203,751	159,818	129,012
Operating expenses:
Research and development expenses	783	4,965	6,108
Selling and marketing expenses	15,425	24,613	15,718
General and administrative expenses	28,614	29,188	28,066
Impairment charge			236,377
Write-off of unsuccessful exploration activities	15,439	4,094	2,639
Operating income (loss)	143,490	96,958	(159,896)
Other income (expense):
Interest income	312	1,332	1,201
Interest expense, net	(84,654)	(73,776)	(64,069)
Foreign currency translation and transaction gains (losses)	(5,839)	5,085	242
Income attributable to sale of tax benefits	24,143	19,945	10,127
Gain from sale of property, plant and equipment	7,628
Other non-operating income, net	756	1,592	590
Income (loss) from continuing operations, before income taxes and equity in income of investees	85,836	51,136	(211,805)
Income tax provision	(27,608)	(13,552)	(1,827)
Equity in losses of investees, net	(3,213)	(250)	(2,522)
Income (loss) from continuing operations	55,015	37,334	(216,154)
Discontinued operations:
Income from discontinued operations (including gain on disposal of $0, $3,646 and $0, respectively)		5,311	4,811
Total income from discontinued operations		4,697	3,547
Net income (loss)	55,015	42,031	(212,607)
Net loss attributable to noncontrolling interest	(833)	(793)	(414)
Net income (loss) attributable to the Company's stockholders	54,182	41,238	(213,021)
Comprehensive income (loss):
Net income (loss)	55,015	42,031	(212,607)
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	(6,302)
Loss in respect of derivative instruments designated for cash flow hedge	(902)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge	(141)	(164)	(190)
Change in unrealized gains or losses on marketable securities available-for-sale			246
Comprehensive income (loss)	47,670	41,867	(212,551)
Comprehensive loss attributable to noncontrolling interest	(833)	(793)	(414)
Comprehensive income (loss) attributable to the Company's stockholders	46,837	41,074	(212,965)
Basic:
Income (loss) from continuing operations (in Dollars per share)	$ 1.19	$ 0.81	$ (4.77)
Discontinued operations (in Dollars per share)		$ 0.10	$ 0.08
Net income (loss) (in Dollars per share)	$ 1.19	$ 0.91	$ (4.69)
Diluted:
Income (loss) from continuing operations (in Dollars per share)	$ 1.18	$ 0.81	$ (4.77)
Discontinued operations (in Dollars per share)		$ 0.10	$ 0.08
Net income (loss) (in Dollars per share)	$ 1.18	$ 0.91	$ (4.69)
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in Shares)	45,508	45,440	45,431
Diluted (in Shares)	45,859	45,475	45,431
Dividend per share declared (in Dollars per share)	$ 0.21	$ 0.08	$ 0.08
Discontinued Operations [Member]
Other income (expense):
Income tax provision		$ (614)	$ (1,264)