Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 74,256	$ 39,617
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	30,553	27,059
Accretion of asset retirement obligation	529	455
Stock-based compensation	1,707	1,713
Amortization of deferred lease income	(671)	(671)
Income attributable to sale of tax benefits, net of interest expense	(6,295)	(4,335)
Equity in losses (earnings) of investees	(1,210)	1,600
Mark-to-market of derivative instruments	962	(1,519)
Write-off of unsuccessful exploration activities	123	0
Gain on severance pay fund asset	129	(947)
Deferred income tax provision and deferred charges	(29,467)	6,612
Liability for unrecognized tax benefits	184	692
Deferred lease revenues	(104)	(92)
Changes in operating assets and liabilities, net of amounts acquired:
Receivables	9,777	19,092
Costs and estimated earnings in excess of billings on uncompleted contracts	(189)	(4,352)
Inventories	(503)	(5,800)
Prepaid expenses and other	(2,005)	6,873
Deposits and other	62	(557)
Accounts payable and accrued expenses	(49,027)	681
Billings in excess of costs and estimated earnings on uncompleted contracts	9,783	14,035
Liabilities for severance pay	(267)	930
Other long-term liabilities	1,008	(1,553)
Net cash provided by operating activities	19,769	71,463
Cash flows from investing activities:
Capital expenditures	(66,962)	(52,885)
Investment in unconsolidated companies	(1,275)	(14,918)
Cash paid for acquisition of controlling interest in a subsidiary, net of cash acquired		(35,300)
Decrease (increase) in severance pay fund asset, net of payments made to retired employees	203	(18)
Net cash used in investing activities	(68,034)	(103,121)
Cash flows from financing activities:
Proceeds from long-term loans, net of transaction costs	100,000
Proceeds from revolving credit lines with banks	860,800	50,000
Repayment of revolving credit lines with banks	(873,800)	(20,000)
Cash received from noncontrolling interest	4,134	1,411
Repayments of long-term debt	(16,687)	(13,405)
Cash paid to noncontrolling interest	(4,674)	(6,807)
Payments of capital leases	(436)	(408)
Deferred debt issuance costs	(1,020)	(1,144)
Cash dividends paid	(11,640)	(8,448)
Net cash provided by financing activities	56,677	1,199
Net change in cash and cash equivalents and restricted cash and cash equivalents	8,412	(30,459)
Cash and cash equivalents and restricted cash and cash equivalentsat beginning of period	96,643	264,476
Cash and cash equivalents and restricted cash and cash equivalents at end of period	105,055	234,017
Supplemental non-cash investing and financing activities:
Increase (decrease) in accounts payable related to purchases of property, plant and equipment	$ (1,673)	$ 1,801