Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Revenue		$ 719,267	$ 692,812	$ 662,591
Revenues	[1]	719,267	692,812	662,591
Cost of revenues:
Cost of revenues		448,832	424,360	391,796
Gross profit		270,435	268,452	270,795
Operating expenses:
Research and development expenses		4,183	3,157	2,762
Selling and marketing expenses		19,802	15,600	16,424
General and administrative expenses		47,750	42,881	46,710
Impairment charge		13,464
Write-off of unsuccessful exploration activities		126	1,796	3,017
Operating income		185,110	205,018	201,882
Other income (expense):
Interest income		974	988	971
Interest expense, net		(70,924)	(54,142)	(67,389)
Derivatives and foreign currency transaction gains (losses)		(4,761)	2,654	(5,534)
Income attributable to sale of tax benefits		19,003	17,878	16,503
Other non-operating income (expense), net		7,779	(1,666)	(5,345)
Income from continuing operations before income taxes and equity in earnings (losses) of investees		137,181	170,730	141,088
Income tax (provision) benefit		(34,733)	(21,664)	(37,059)
Equity in earnings (losses) of investees, net		7,663	(1,957)	(7,735)
Income from continuing operations		110,111	147,109	96,294
Net income attributable to noncontrolling interest		(12,145)	(14,695)	(7,586)
Net income attributable to the Company's stockholders		97,966	132,414	88,708
Comprehensive income:
Net income		110,111	147,109	96,294
Other comprehensive income (loss), net of related taxes:
Currency translation adjustments		(1,831)	3,440	(1,648)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment		2,235	804	1,185
Loss in respect of derivative instruments designated for cash flow hedge		81	135	141
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge		(57)	(73)	(96)
Comprehensive income		110,539	151,415	95,876
Comprehensive income attributable to noncontrolling interest		(11,666)	(15,532)	(7,179)
Comprehensive income attributable to the Company's stockholders		$ 98,873	$ 135,883	$ 88,697
Basic:
Net income (in dollars per share)		$ 1.93	$ 2.64	$ 1.79
Diluted:
Net income (in dollars per share)		$ 1.92	$ 2.61	$ 1.77
Weighted average number of shares used in computation of earnings per share attributable to the Company's stockholders:
Basic (in shares)		50,643	50,110	49,469
Diluted (in shares)		50,969	50,769	50,140
Electricity [Member]
Revenues:
Revenue		$ 509,879	$ 465,593	$ 436,292
Cost of revenues:
Cost of revenues		298,255	266,840	261,573
Product [Member]
Revenues:
Revenue		201,743	224,483	226,299
Cost of revenues:
Cost of revenues		140,697	152,094	130,223
Other Revenue [Member]
Revenues:
Revenue		7,645	2,736
Cost of revenues:
Cost of revenues		$ 9,880	$ 5,426

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