Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 79,416,000	$ 87,022,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	111,328,000	98,371,000
Accretion of asset retirement obligation	2,015,000	1,826,000
Stock-based compensation	7,231,000	7,382,000
Amortization of deferred lease income	(2,014,000)	(2,014,000)
Income attributable to sale of tax benefits, net of interest expense	(7,738,000)	(9,806,000)
Equity in losses (earnings) of investees	(3,334,000)	(1,774,000)
Mark-to-market of derivative instruments	(1,909,000)	1,202,000
Loss on disposal of property, plant and equipment	1,426,000	5,365,000
Write-off of unsuccessful exploration activities	0	119,000
Loss (gain) on severance pay fund asset	(862,000)	630,000
Deferred income tax provision	7,177,000	(6,612,000)
Liability for unrecognized tax benefits	3,284,000	1,249,000
Deferred lease revenues	(470,000)	(303,000)
Gain from insurance recoveries	0	(7,150,000)
Changes in operating assets and liabilities, net of businesses acquired:
Receivables	(60,000)	(9,704,000)
Costs and estimated earnings in excess of billings on uncompleted contracts	(995,000)	(6,866,000)
Inventories	3,780,000	(1,728,000)
Prepaid expenses and other	4,003,000	(4,183,000)
Operating lease right of use asset	5,620,000	0
Deposits and other	(2,622,000)	10,000
Accounts payable and accrued expenses	14,237,000	(50,056,000)
Billings in excess of costs and estimated earnings on uncompleted contracts	(12,399,000)	1,519,000
Liabilities for severance pay	576,000	(1,238,000)
Other long-term liabilities	(6,238,000)	(105,000)
Net cash provided by operating activities	201,452,000	103,156,000
Cash flows from investing activities:
Capital expenditures	(190,530,000)	(200,657,000)
Cash received from insurance recoveries related to destroyed equipment	0	7,150,000
Investment in unconsolidated companies	(3,096,000)	(3,800,000)
Cash paid for acquisition of controlling interest in a subsidiary, net of cash acquired	0	(95,093,000)
Decrease (increase) in severance pay fund asset, net of payments made to retired employees	615,000	850,000
Net cash used in investing activities	(193,011,000)	(291,550,000)
Cash flows from financing activities:
Proceeds from sale of membership interests to noncontrolling interest, net of transaction costs	0	3,174,000
Proceeds from long-term loans, net of transaction costs	132,847,000	100,000,000
Proceeds from exercise of options by employees	2,057,000	0
Proceeds from issuance of senior unsecured notes, net of transaction costs	0	0
Purchase of Senior unsecured notes	0	0
Proceeds from the sale of limited liability company interest, net of transaction costs	58,671,000	32,403,000
Prepayment of loans	(6,098,000)	0
Proceeds from issuance of commercial paper	50,000,000	0
Proceeds from revolving credit lines with banks	1,311,500,000	2,819,800,000
Repayment of revolving credit lines with banks	(1,470,500,000)	(2,661,800,000)
Cash received from noncontrolling interest	3,346,000	4,134,000
Repayments of long-term debt	(52,997,000)	(41,858,000)
Cash paid to noncontrolling interest	(9,399,000)	(9,555,000)
Payments of finance leases	(2,734,000)	(1,706,000)
Deferred debt issuance costs	(4,566,000)	(3,002,000)
Cash dividends paid	(16,774,000)	(21,766,000)
Net cash provided by (used in) financing activities	(4,647,000)	219,824,000
Effect of exchange rate changes	(1,252,000)	0
Net change in cash and cash equivalents and restricted cash and cash equivalents	2,542,000	31,430,000
Restricted cash and cash equivalents acquired in a business combination	0	26,993,000
Cash and cash equivalents and restricted cash and cash equivalents at beginning of period	177,495,000	96,643,000
Cash and cash equivalents and restricted cash and cash equivalents at end of period	180,037,000	155,066,000
Supplemental non-cash investing and financing activities:
Increase (decrease) in accounts payable related to purchases of property, plant and equipment	7,496,000	(10,390,000)
Right of use assets obtained in exchange for new lease liabilities	$ 10,435,000	$ 5,864,000