Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 70,284,000	$ 99,201,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	77,565,000	80,463,000
Amortization of premium from senior unsecured bonds	(513,000)	(230,000)
Accretion of asset retirement obligation	1,243,000	1,140,000
Stock-based compensation	3,383,000	3,077,000
Amortization of deferred lease income	(2,014,000)	(2,014,000)
Income attributable to sale of tax benefits, net of interest expense	(5,920,000)	(13,068,000)
Equity in losses of investees	4,735,000	4,893,000
Mark-to-market of derivative instruments	(381,000)	3,906,000
Loss on disposal of property, plant and equipment		531,000
Write-off of unsuccessful exploration activities	2,714,000	359,000
Gain on severance pay fund asset	(690,000)	(102,000)
Deferred income tax provision	20,742,000	(34,613,000)
Liability for unrecognized tax benefits	(125,000)	(399,000)
Deferred lease revenues	(625,000)	(221,000)
Other		484,000
Changes in operating assets and liabilities, net of amounts acquired:
Receivables	(13,711,000)	(2,879,000)
Costs and estimated earnings in excess of billings on uncompleted contracts	(12,905,000)	13,334,000
Inventories	5,339,000	335,000
Prepaid expenses and other	(5,364,000)	(3,033,000)
Deposits and other	(867,000)	(294,000)
Accounts payable and accrued expenses	10,463,000	(21,904,000)
Due from/to related entities, net		451,000
Billings in excess of costs and estimated earnings on uncompleted contracts	(3,242,000)	2,108,000
Liabilities for severance pay	(369,000)	(1,573,000)
Other long-term liabilities	1,801,000	(2,259,000)
Due from/to Parent		(513,000)
Net cash provided by operating activities	158,027,000	122,965,000
Cash flows from investing activities:
Cash acquired in organizational restructuring and share exchange with parent		15,391,000
Net change in restricted cash, cash equivalents and marketable securities	(1,022,000)	22,725,000
Capital expenditures	(107,951,000)	(117,588,000)
Cash paid for acquisition of controlling interest in a subsidiary, net of cash acquired	(18,135,000)
Decrease in severance pay fund asset, net of payments made to retired employees	1,919,000	2,934,000
Net cash used in investing activities	(125,189,000)	(76,538,000)
Cash flows from financing activities:
Proceeds from exercise of options by employees	7,250,000	4,612,000
Proceeds from issuance of senior unsecured notes, net of transaction costs	203,483,000
Purchase of Senior unsecured notes	(249,468,000)
Purchase of OFC Senior Secured Notes	(6,815,000)	(30,638,000)
Proceeds from sale of membership interests to uncontrolling interest, net of transaction costs		156,761,000
Proceeds from long-term loans, net at transaction costs		42,000,000
Proceeds from revolving credit lines with banks	259,900,000	598,800,000
Repayment of revolving credit lines with banks	(259,900,000)	(619,100,000)
Cash received from non-controlling interest	1,972,000	1,654,000
Repayments of long-term debt	(40,997,000)	(40,532,000)
Cash paid to noncontrolling interest	(17,296,000)	(13,863,000)
Payments of capital leases	(845,000)
Deferred debt issuance costs	(3,506,000)	(5,038,000)
Cash dividends paid	(22,469,000)	(9,772,000)
Net cash provided by (used in) financing activities	(128,691,000)	84,884,000
Net change in cash and cash equivalents	(95,853,000)	131,311,000
Cash and cash equivalents at beginning of period	185,919,000	40,230,000
Cash and cash equivalents at end of period	90,066,000	171,541,000
Supplemental non-cash investing and financing activities:
Increase (decrease) in accounts payable related to purchases of property, plant and equipment	(4,517,000)	18,930,000
Accrued liabilities related to financing activities	$ 6,291,000