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																							5,343			5,343		5,343
Exercise of options by employees and directors (in shares)																						243
Exercise of options by employees and directors																							785			785		785
Cash paid to noncontrolling interest																											(14,594)	(14,594)
Cash dividend declared																								(12,426)		(12,426)		(12,426)
Net income																								43,834		43,834	6,941	50,775
Currency translation adjustment																									1,143	1,143	396	1,539
Loss in respect of derivative instruments designated for cash flow hedge																									93	93		93
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)																									(347)	(347)		(347)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge																									(39)	(39)		(39)
Balance (in shares) at Jun. 30, 2017																						49,910
Balance at Jun. 30, 2017																						$ 50	875,591	246,760	(7,325)	1,115,076	84,325	1,199,401
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																							3,823			3,823		3,823
Exercise of options by employees and directors (in shares)																						21
Exercise of options by employees and directors
Cash paid to noncontrolling interest																											(6,377)	(6,377)
Cash dividend declared																								(16,702)		(16,702)		(16,702)
Net income																								69,165		69,165	7,289	76,454
Currency translation adjustment																									(764)	(764)	(204)	(968)
Loss in respect of derivative instruments designated for cash flow hedge																									40	40		40
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)																									3,163	3,163		3,163
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge																									(30)	(30)		(30)
Cumulative effect of changes in accounting principles at Dec. 31, 2017																								25,635		25,635		25,635
Increase in noncontrolling interest						$ 2,165	$ 2,165						$ 996	$ 996						$ 34,898	$ 34,898
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