Property, Plant and Equipment, Net (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Land owned by the Company where the geothermal resource is located	$ 32,396	$ 32,411
Leasehold improvements	1,339	1,325
Machinery and equipment	100,499	92,227
Office equipment	15,218	16,444
Automobiles	5,816	5,581
Geothermal and recovered energy generation power plants, including geothermal wells and exploration and resource development costs:
Asset retirement cost	7,214	9,441
Property, Plant and Equipment, Gross	1,771,428	1,973,326
Less accumulated depreciation	(544,670)	(454,794)
Property, plant and equipment, net	1,226,758	1,518,532
United States of America
Geothermal and recovered energy generation power plants, including geothermal wells and exploration and resource development costs:
Geothermal and recovered energy generation power plants, including geothermal wells and exploration and resource development costs	1,296,534	1,534,001
Foreign countries
Geothermal and recovered energy generation power plants, including geothermal wells and exploration and resource development costs:
Geothermal and recovered energy generation power plants, including geothermal wells and exploration and resource development costs	$ 312,412	$ 281,896