Condensed Consolidated Statements of Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Guadeloupe 1 [Member] Noncontrolling Interest [Member]	Guadeloupe 1 [Member]	Tungsten [Member] Noncontrolling Interest [Member]	Tungsten [Member]	U.S. Geothermal [Member] Noncontrolling Interest [Member]	U.S. Geothermal [Member]	McGinness Hills Phase III [Member] Noncontrolling Interest [Member]	McGinness Hills Phase III [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Parent [Member]	Noncontrolling Interest [Member]	Total
Balance (in shares) at Dec. 31, 2017									50,609
Balance at Dec. 31, 2017									$ 51	$ 888,778	$ 327,255	$ (4,706)	$ 1,211,378	$ 84,322	$ 1,295,700
Cumulative effect of changes in accounting principles at Dec. 31, 2017											25,635		25,635		25,635
Adjusted balance as of the beginning of the year at Dec. 31, 2017									$ 51	888,778	352,890	(4,706)	1,237,013	84,322	1,321,335
Stock-based compensation										1,707			1,707		1,707
Exercise of options by employees and directors (in shares)									8
Cash paid to noncontrolling interest														(4,674)	(4,674)
Cash dividend declared											(11,640)		(11,640)		(11,640)
Net income											69,508		69,508	4,482	73,990
Currency translation adjustment												1,158	1,158	370	1,528
Loss in respect of derivative instruments designated for cash flow hedge												20	20		20
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment												2,634	2,634		2,634
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge												(15)	(15)		(15)
Change in foreign currency translation adjustments												1,158	1,158	370	1,528
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment												2,634	2,634		2,634
Balance (in shares) at Mar. 31, 2018									50,617
Balance at Mar. 31, 2018									$ 51	890,485	410,758	(909)	1,300,385	84,500	1,384,885
Balance (in shares) at Dec. 31, 2017									50,609
Balance at Dec. 31, 2017									$ 51	888,778	327,255	(4,706)	1,211,378	84,322	1,295,700
Cumulative effect of changes in accounting principles at Dec. 31, 2017											25,635		25,635		25,635
Adjusted balance as of the beginning of the year at Dec. 31, 2017									$ 51	888,778	352,890	(4,706)	1,237,013	84,322	1,321,335
Currency translation adjustment															(1,059)
Loss in respect of derivative instruments designated for cash flow hedge															60
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment															4,175
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge															(44)
Change in foreign currency translation adjustments															(1,059)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment															4,175
Balance (in shares) at Sep. 30, 2018									50,630
Balance at Sep. 30, 2018									$ 51	896,160	410,870	(1,386)	1,305,695	124,001	1,429,696
Balance (in shares) at Mar. 31, 2018									50,617
Balance at Mar. 31, 2018									$ 51	890,485	410,758	(909)	1,300,385	84,500	1,384,885
Adjusted balance as of the beginning of the year at Mar. 31, 2018									$ 51	890,485	410,758	(909)	1,300,385	84,500	1,384,885
Stock-based compensation										2,116			2,116		2,116
Exercise of options by employees and directors (in shares)									13
Cash paid to noncontrolling interest														(1,703)	(1,703)
Cash dividend declared											(5,062)		(5,062)		(5,062)
Net income											(343)		(343)	2,807	2,464
Currency translation adjustment												(1,922)	(1,922)	(574)	(2,496)
Loss in respect of derivative instruments designated for cash flow hedge												20	20		20
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment												529	529		529
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge												(15)	(15)		(15)
Increase in noncontrolling interest	$ 2,165	$ 2,165	$ 996	$ 996	$ 34,898	$ 34,898
Change in foreign currency translation adjustments												(1,922)	(1,922)	(574)	(2,496)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment												529	529		529
Balance (in shares) at Jun. 30, 2018									50,630
Balance at Jun. 30, 2018									$ 51	892,601	405,353	(2,297)	1,295,708	123,089	1,418,797
Stock-based compensation										3,559			3,559		3,559
Cash paid to noncontrolling interest														(1,525)	(1,525)
Cash dividend declared											(5,064)		(5,064)		(5,064)
Net income											10,581		10,581	(753)	9,828
Currency translation adjustment												(107)	(107)	16	(91)
Loss in respect of derivative instruments designated for cash flow hedge												20	20		20
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment												1,012	1,012		1,012
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge												(14)	(14)		(14)
Increase in noncontrolling interest	$ 3,174	$ 3,174
Change in foreign currency translation adjustments												(107)	(107)	16	(91)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment												1,012	1,012		1,012
Balance (in shares) at Sep. 30, 2018									50,630
Balance at Sep. 30, 2018									$ 51	896,160	410,870	(1,386)	1,305,695	124,001	1,429,696
Balance (in shares) at Dec. 31, 2018									50,700
Balance at Dec. 31, 2018									$ 51	901,363	422,222	(3,799)	1,319,837	125,259	1,445,096
Cumulative effect of changes in accounting principles at Dec. 31, 2018											(58)		(58)		(58)
Adjusted balance as of the beginning of the year at Dec. 31, 2018									$ 51	901,363	422,164	(3,799)	1,319,779	125,259	1,445,038
Stock-based compensation										2,360			2,360		2,360
Exercise of options by employees and directors (in shares)									52
Cash paid to noncontrolling interest														(4,146)	(4,146)
Cash dividend declared											(5,579)		(5,579)		(5,579)
Net income											25,946		25,946	1,855	27,801
Currency translation adjustment												(1,026)	(1,026)	(322)	(1,348)
Loss in respect of derivative instruments designated for cash flow hedge												22	22		22
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment												(1,145)	(1,145)		(1,145)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge												(8)	(8)		(8)
Change in foreign currency translation adjustments												(1,026)	(1,026)	(322)	(1,348)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment												(1,145)	(1,145)		(1,145)
Balance (in shares) at Mar. 31, 2019									50,752
Balance at Mar. 31, 2019									$ 51	903,723	442,531	(5,956)	1,340,349	122,646	1,462,995
Balance (in shares) at Dec. 31, 2018									50,700
Balance at Dec. 31, 2018									$ 51	901,363	422,222	(3,799)	1,319,837	125,259	1,445,096
Cumulative effect of changes in accounting principles at Dec. 31, 2018											(58)		(58)		(58)
Adjusted balance as of the beginning of the year at Dec. 31, 2018									$ 51	901,363	422,164	(3,799)	1,319,779	125,259	1,445,038
Currency translation adjustment															(3,057)
Loss in respect of derivative instruments designated for cash flow hedge															58
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment															(4,699)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge															(24)
Change in foreign currency translation adjustments															(3,057)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment															(4,699)
Balance (in shares) at Sep. 30, 2019									50,993
Balance at Sep. 30, 2019									$ 51	910,651	480,879	(10,848)	1,380,733	124,055	1,504,788
Balance (in shares) at Mar. 31, 2019									50,752
Balance at Mar. 31, 2019									$ 51	903,723	442,531	(5,956)	1,340,349	122,646	1,462,995
Stock-based compensation										2,643			2,643		2,643
Exercise of options by employees and directors (in shares)									110
Cash paid to noncontrolling interest														(2,767)	(2,767)
Cash dividend declared											(5,589)		(5,589)		(5,589)
Net income											33,938		33,938	2,017	35,955
Currency translation adjustment												298	298	184	482
Loss in respect of derivative instruments designated for cash flow hedge												18	18		18
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment												(2,087)	(2,087)		(2,087)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge												(9)	(9)		(9)
Change in foreign currency translation adjustments												298	298	184	482
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment												(2,087)	(2,087)		(2,087)
Balance (in shares) at Jun. 30, 2019									50,862
Balance at Jun. 30, 2019									$ 51	906,366	470,880	(7,736)	1,369,561	122,080	1,491,641
Stock-based compensation										2,228			2,228		2,228
Exercise of options by employees and directors (in shares)									131
Cash paid to noncontrolling interest														(1,326)	(1,326)
Cash dividend declared											(5,606)		(5,606)		(5,606)
Net income											15,605		15,605	(805)	14,800
Currency translation adjustment											0		(1,656)	(535)	(2,191)
Loss in respect of derivative instruments designated for cash flow hedge												18	18		18
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment												(1,467)	(1,467)		(1,467)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge												(7)	(7)		(7)
Increase in noncontrolling interest							$ 4,641	$ 4,641
Exercise of options by employees and directors										2,057			2,057		2,057
Change in foreign currency translation adjustments											0		(1,656)	(535)	(2,191)
Change in unrealized gains or losses in respect of the Company's share in derivatives instruments of unconsolidated investment												(1,467)	(1,467)		(1,467)
Balance (in shares) at Sep. 30, 2019									50,993
Balance at Sep. 30, 2019									$ 51	$ 910,651	$ 480,879	$ (10,848)	$ 1,380,733	$ 124,055	$ 1,504,788