Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 101,516	$ 123,349	$ 55,015
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	105,977	107,206	100,798
Amortization of premium from senior unsecured bonds	(513)	(306)	(308)
Accretion of asset retirement obligation	1,778	1,198	829
Stock-based compensation	5,157	3,955	5,571
Amortization of deferred lease income	(2,685)	(2,685)	(2,685)
Income attributable to sale of tax benefits, net of interest expense	(6,962)	(17,467)	(13,823)
Equity in losses of investees	7,735	5,508	3,213
Mark-to-market of derivative instruments	319	4,129	(6,960)
Write-off of unsuccessful exploration activities	3,017	1,579	15,439
Gain on severance pay fund asset	(304)	(119)	1,492
Gain on sale of a subsidiary			(7,628)
Deferred income tax provision	18,473	(39,530)	13,135
Liability for unrecognized tax benefits	(4,647)	2,874	2,561
Deferred lease revenues	(853)	224	(251)
Other		484	(181)
Changes in operating assets and liabilities, net of amounts acquired:
Receivables	(33,280)	(3,806)	47,114
Costs and estimated earnings in excess of billings on uncompleted contracts	(27,078)	2,673	(6,576)
Inventories	6,297	(1,144)	5,359
Prepaid expenses and other	(12,540)	(2,579)	(1,337)
Deposits and other	(1,009)	(648)	584
Accounts payable and accrued expenses	(1,375)	(339)	(9,638)
Due from/to related entities, net		451	(9)
Billings in excess of costs and estimated earnings on uncompleted contracts	2,262	(9,168)	(16,821)
Liabilities for severance pay	(786)	(1,076)	(3,442)
Other long-term liabilities	3,310	(2,561)	(903)
Due from/to Parent		(513)	(955)
Net cash provided by operating activities	159,285	190,025	213,235
Cash flows from investing activities:
Cash acquired in organizational restructuring and share exchange with parent		15,391
Net change in restricted cash, cash equivalents and marketable securities	15,241	43,745	(42,183)
Cash received from sale of a subsidiary			35,250
Capital expenditures	(151,930)	(152,450)	(151,153)
Cash grant received from the U.S. Treasury under Section 1603 of the ARRA			27,427
Investment in unconsolidated companies	(3,569)		(631)
Cash paid for acquisition of controlling interest in a subsidiary, net of cash acquired	(20,135)
Intangible assets acquired		(500)
Decrease in severance pay fund asset, net of payments made to retired employees	1,862	2,843	2,128
Net cash used in investing activities	(158,531)	(90,971)	(129,162)
Cash flows from financing activities:
Proceeds from sale of membership interests to noncontrolling interest, net of transaction costs	44,102	156,635
Proceeds from long-term loans, net of transaction costs	142,500	42,000	140,000
Proceeds from exercise of options by employees	7,249	6,085	981
Proceeds from issuance of senior unsecured notes, net of transaction costs	203,483
Purchase of Senior unsecured notes	(249,468)
Cash received from noncontrolling interest	1,972	1,654	2,234
Purchase of OFC Senior Secured Notes	(6,815)	(30,638)	(12,860)
Proceeds from revolving credit lines with banks	309,400	598,800	2,830,683
Repayment of revolving credit lines with banks	(309,400)	(619,100)	(2,922,400)
Cash received from noncontrolling interest	1,972	1,654	2,234
Payment for acquisition of noncontrolling interest in Crump			(1,490)
Repayments of long-term debt	(62,052)	(71,701)	(111,180)
Cash paid to noncontrolling interest	(64,065)	(19,068)	(11,320)
Cash paid for interest rate cap			(1,505)
Payments of capital leases	(1,178)
Deferred debt issuance costs	(6,402)	(5,316)	(4,785)
Cash dividends paid	(25,682)	(12,716)	(9,555)
Net cash provided by (used in) financing activities	43,541	46,635	(101,197)
Net change in cash and cash equivalents	44,295	145,689	(17,124)
Cash and cash equivalents at beginning of period	185,919	40,230	57,354
Cash and cash equivalents at end of period	230,214	185,919	40,230
Cash paid during the year for:
Interest, net of interest capitalized	55,366	55,492	62,376
Income taxes, net	18,490	10,419	5,787
Supplemental non-cash investing and financing activities:
Increase (decrease) in accounts payable related to purchases of property, plant and equipment	(2,219)	3,810	3,853
Accrued liabilities related to financing activities	6,291	1,665	658
Increase (decrease) in asset retirement cost and asset retirement obligation	714	516	(366)
Opal Transaction [Member]
Cash flows from financing activities:
Cash received from noncontrolling interest	59,897
Cash received from noncontrolling interest	$ 59,897