Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 100,757,000	$ 70,284,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	81,010,000	77,565,000
Amortization of premium from senior unsecured bonds		(513,000)
Accretion of asset retirement obligation	1,392,000	1,243,000
Stock-based compensation	7,204,000	3,383,000
Amortization of deferred lease income	(2,014,000)	(2,014,000)
Income attributable to sale of tax benefits, net of interest expense	(8,851,000)	(5,920,000)
Equity in losses of investees	1,690,000	4,735,000
Mark-to-market of derivative instruments	(764,000)	(381,000)
Write-off of unsuccessful exploration activities	0	2,714,000
Gain on severance pay fund asset	(1,463,000)	(690,000)
Deferred income tax provision	16,506,000	20,742,000
Liability for unrecognized tax benefits	450,000	(125,000)
Deferred lease revenues	(274,000)	(625,000)
Other	501,000
Changes in operating assets and liabilities, net of amounts acquired:
Receivables	(10,808,000)	(13,711,000)
Costs and estimated earnings in excess of billings on uncompleted contracts	10,111,000	(12,905,000)
Inventories	(209,000)	5,339,000
Prepaid expenses and other	(636,000)	(5,364,000)
Deposits and other	1,231,000	(867,000)
Accounts payable and accrued expenses	(3,655,000)	10,463,000
Billings in excess of costs and estimated earnings on uncompleted contracts	25,344,000	(3,242,000)
Liabilities for severance pay	1,764,000	(369,000)
Other long-term liabilities	(2,065,000)	1,801,000
Net cash provided by operating activities	166,533,000	158,027,000
Cash flows from investing activities:
Net change in restricted cash, cash equivalents and marketable securities	(8,297,000)	(1,022,000)
Capital expenditures	(177,410,000)	(107,951,000)
Investment in unconsolidated companies	(37,867,000)
Buyout of Class B membership in ORTP	(2,357,000)
Cash paid for acquisition of controlling interest in a subsidiary, net of cash acquired	(35,300,000)	(18,135,000)
Intangible assets acquired	(868,000)
Decrease (increase) in severance pay fund asset, net of payments made to retired employees	529,000	1,919,000
Net cash used in investing activities	(261,570,000)	(125,189,000)
Cash flows from financing activities:
Proceeds from exercise of options by employees	16,382,000	7,250,000
Proceeds from issuance of senior unsecured notes, net of transaction costs		203,483,000
Purchase of Senior unsecured notes		(249,468,000)
Prepayment of OFC Senior Secured Notes	(14,270,000)	(6,815,000)
Proceeds from revolving credit lines with banks	695,600,000	259,900,000
Repayment of revolving credit lines with banks	(661,700,000)	(259,900,000)
Cash received from noncontrolling interest	2,017,000	1,972,000
Repayments of long-term debt	(55,226,000)	(40,997,000)
Cash paid to noncontrolling interest	(18,032,000)	(17,296,000)
Payments of capital leases	(1,472,000)	(845,000)
Deferred debt issuance costs	(4,652,000)	(3,506,000)
Cash dividends paid	(16,612,000)	(22,469,000)
Net cash used in financing activities	(57,965,000)	(128,691,000)
Net change in cash and cash equivalents	(153,002,000)	(95,853,000)
Cash and cash equivalents at beginning of period	230,214,000	185,919,000
Cash and cash equivalents at end of period	77,212,000	90,066,000
Supplemental non-cash investing and financing activities:
Increase (decrease) in accounts payable related to purchases of property, plant and equipment	982,000	(4,517,000)
Accrued liabilities related to financing activities		$ 6,291,000