Consolidated Statements of Equity (Unaudited) - USD ($) $ in Thousands	Guadeloupe [Member] Common Stock [Member]	Guadeloupe [Member] Additional Paid-in Capital [Member]	Guadeloupe [Member] Retained Earnings [Member]	Guadeloupe [Member] AOCI Attributable to Parent [Member]	Guadeloupe [Member] Parent [Member]	Guadeloupe [Member] Noncontrolling Interest [Member]	Guadeloupe [Member]	Tungsten [Member] Common Stock [Member]	Tungsten [Member] Additional Paid-in Capital [Member]	Tungsten [Member] Retained Earnings [Member]	Tungsten [Member] AOCI Attributable to Parent [Member]	Tungsten [Member] Parent [Member]	Tungsten [Member] Noncontrolling Interest [Member]	Tungsten [Member]	U.S. Geothermal [Member] Common Stock [Member]	U.S. Geothermal [Member] Additional Paid-in Capital [Member]	U.S. Geothermal [Member] Retained Earnings [Member]	U.S. Geothermal [Member] AOCI Attributable to Parent [Member]	U.S. Geothermal [Member] Parent [Member]	U.S. Geothermal [Member] Noncontrolling Interest [Member]	U.S. Geothermal [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, 2016																						49,667
Balance at Dec. 31, 2016																						$ 50	$ 869,463	$ 215,352	$ (8,175)	$ 1,076,690	$ 91,582	$ 1,168,272
Stock-based compensation																							7,204			7,204		7,204
Exercise of options by employees and directors (in shares)																						930
Exercise of options by employees and directors																						$ 1	16,382			16,383		16,383
Cash paid to noncontrolling interest																											(18,032)	(18,032)
Cash dividend declared																								(16,612)		(16,612)		(16,612)
Buyout of class B membership in ORTP																							2,956			2,956	(6,964)	(4,008)
Net income																								67,794		67,794	10,154	77,948
Other comprehensive income (loss), net of related taxes:
Currency translation adjustment																									1,822	1,822	722	2,544
Loss in respect of derivative instruments designated for cash flow hedge																									113	113		113
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment (net of related tax of $0)																									271	271		271
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge																									(57)	(57)		(57)
Balance (in shares) at Dec. 31, 2016																						49,667
Balance at Dec. 31, 2016																						$ 50	869,463	215,352	(8,175)	1,076,690	91,582	1,168,272
Other comprehensive income (loss), net of related taxes:
Stock-based compensation																							7,204			7,204		7,204
Exercise of options by employees and directors (in shares)																						930
Exercise of options by employees and directors																						$ 1	16,382			16,383		16,383
Cash paid to noncontrolling interest																											(18,032)	(18,032)
Cash dividend declared																								(16,612)		(16,612)		(16,612)
Net income																								67,794		67,794	10,154	77,948
Balance (in shares) at Sep. 30, 2017																						50,597
Balance at Sep. 30, 2017																						$ 51	896,005	266,534	(6,026)	1,156,564	77,462	1,234,026
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
Stock-based compensation																							7,382			7,382		7,382
Exercise of options by employees and directors (in shares)																						21
Exercise of options by employees and directors
Cash paid to noncontrolling interest																											(7,902)	(7,902)
Cash dividend declared																								(21,766)		(21,766)		(21,766)
Net income																								79,746		79,746	6,536	86,282
Other comprehensive income (loss), net of related taxes:
Currency translation adjustment																									(871)	(871)	(188)	(1,059)
Loss in respect of derivative instruments designated for cash flow hedge																									60	60		60
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment (net of related tax of $0)																									4,175	4,175		4,175
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge																									(44)	(44)		(44)
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
Other comprehensive income (loss), net of related taxes:
Stock-based compensation																							7,382			7,382		7,382
Exercise of options by employees and directors (in shares)																						21
Exercise of options by employees and directors
Cumulative effect of changes in accounting principles at Dec. 31, 2017																								25,635		25,635		25,635
Other comprehensive income (loss), net of related taxes:
Cash paid to noncontrolling interest																											(7,902)	(7,902)
Cash dividend declared																								(21,766)		(21,766)		(21,766)
Increase in noncontrolling interest						$ 5,339	$ 5,339						$ 996	$ 996						$ 34,898	$ 34,898
Net income																								79,746		79,746	6,536	86,282
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