Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 77,977,000	$ 55,878,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	54,082,000	51,258,000
Amortization of premium from senior unsecured bonds		(154,000)
Accretion of asset retirement obligation	919,000	821,000
Stock-based compensation	5,343,000	1,659,000
Amortization of deferred lease income	(1,343,000)	(1,343,000)
Income attributable to sale of tax benefits, net of interest expense	(6,844,000)	(5,076,000)
Equity in losses of investees	2,027,000	2,081,000
Mark-to-market of derivative instruments	(2,462,000)	(162,000)
Write-off of unsuccessful exploration activities	0	1,420,000
Gain on severance pay fund asset	(1,537,000)	(253,000)
Deferred income tax provision	8,375,000	13,254,000
Liability for unrecognized tax benefits	277,000	(411,000)
Deferred lease revenues	(182,000)	169,000
Changes in operating assets and liabilities, net of amounts acquired:
Receivables	(625,000)	(10,206,000)
Costs and estimated earnings in excess of billings on uncompleted contracts	(7,703,000)	9,861,000
Inventories	(103,000)	1,384,000
Prepaid expenses and other	1,820,000	(11,007,000)
Deposits and other	652,000	(153,000)
Accounts payable and accrued expenses	(4,636,000)	1,808,000
Billings in excess of costs and estimated earnings on uncompleted contracts	14,056,000	(9,020,000)
Liabilities for severance pay	2,425,000	(297,000)
Other long-term liabilities	(248,000)	22,000
Net cash provided by operating activities	114,158,000	119,573,000
Cash flows from investing activities:
Net change in restricted cash, cash equivalents and marketable securities	(15,248,000)	11,498,000
Capital expenditures	(116,015,000)	(67,779,000)
Investment in unconsolidated companies	(27,412,000)
Cash paid for acquisition of controlling interest in a subsidiary, net of cash acquired	(35,300,000)
Decrease (increase) in severance pay fund asset, net of payments made to retired employees	(130,000)	992,000
Net cash used in investing activities	(194,105,000)	(55,289,000)
Cash flows from financing activities:
Proceeds from exercise of options by employees	785,000	5,945,000
Proceeds from revolving credit lines with banks	437,500,000	134,500,000
Repayment of revolving credit lines with banks	(407,500,000)	(134,500,000)
Cash received from noncontrolling interest	2,017,000	1,972,000
Repayments of long-term debt	(33,177,000)	(31,386,000)
Cash paid to noncontrolling interest	(14,594,000)	(12,249,000)
Payments of capital leases	(751,000)
Deferred debt issuance costs	(3,731,000)	(2,931,000)
Cash dividends paid	(12,426,000)	(18,998,000)
Net cash provided by (used in) financing activities	(31,877,000)	(57,647,000)
Net change in cash and cash equivalents	(111,824,000)	6,637,000
Cash and cash equivalents at beginning of period	230,214,000	185,919,000
Cash and cash equivalents at end of period	118,390,000	192,556,000
Supplemental non-cash investing and financing activities:
Increase (decrease) in accounts payable related to purchases of property, plant and equipment	2,338,000	(6,956,000)
Accrued liabilities related to financing activities		$ 6,128,000