Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Revenues	[1]	$ 692,812	$ 662,591	$ 594,644
Cost of revenues:
Cost of revenues		424,360	391,796	376,365
Gross profit		268,452	270,795	218,279
Operating expenses:
Research and development expenses		3,157	2,762	1,780
Selling and marketing expenses		15,600	16,424	16,077
General and administrative expenses		42,881	46,710	34,782
Write-off of unsuccessful exploration activities		1,796	3,017	1,579
Operating income		205,018	201,882	164,061
Other income (expense):
Interest income		988	971	297
Interest expense, net		(54,142)	(67,389)	(72,577)
Derivatives and foreign currency transaction gains (losses)		2,654	(5,534)	(1,622)
Income attributable to sale of tax benefits		17,878	16,503	25,431
Other non-operating expense, net		(1,666)	(5,345)	(1,991)
Income from continuing operations before income taxes and equity in losses of investees		170,730	141,088	113,599
Income tax (provision) benefit		(21,664)	(37,059)	16,057
Equity in earnings (losses) of investees, net		(1,957)	(7,735)	(5,508)
Income from continuing operations		147,109	96,294	124,148
Net income attributable to noncontrolling interest		(14,695)	(7,586)	(3,776)
Net income attributable to the Company's stockholders		132,414	88,708	120,372
Comprehensive income:
Net income		147,109	96,294	124,148
Other comprehensive income (loss), net of related taxes:
Currency translation adjustments		3,440	(1,648)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment		804	1,185	1,028
Loss in respect of derivative instruments designated for cash flow hedge		135	141	147
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge		(73)	(96)	(118)
Comprehensive income		151,415	95,876	125,205
Comprehensive income attributable to noncontrolling interest		(15,532)	(7,179)	(3,776)
Comprehensive income attributable to the Company's stockholders		$ 135,883	$ 88,697	$ 121,429
Basic:
Basic: (in dollars per share)		$ 2.64	$ 1.79	$ 2.48
Diluted:
Net income (in dollars per share)		$ 2.61	$ 1.77	$ 2.45
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in shares)		50,110	49,469	48,562
Diluted (in shares)		50,769	50,140	49,187
Dividend per share declared (in dollars per share)		$ 0.41	$ 0.52	$ 0.26
Electricity [Member]
Revenues:
Revenues		$ 468,329	$ 436,292	$ 375,920
Cost of revenues:
Cost of revenues		272,266	261,573	242,612
Product [Member]
Revenues:
Revenues		224,483	226,299	218,724
Cost of revenues:
Cost of revenues		$ 152,094	$ 130,223	$ 133,753

[1] Revenues as reported in the geographic area in which they originate.