Quarterly Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Revenues:
Electricity	$ 78,819	$ 81,452	$ 85,011	$ 82,247	$ 77,576	$ 86,815	$ 81,190	$ 78,268	$ 327,529		$ 323,849		$ 291,820
Product	37,263	54,685	44,826	50,105	46,158	24,026	23,424	19,552	186,879		113,160		81,410
Total revenues	116,082	136,137	129,837	132,352	123,734	110,841	104,614	97,820	514,408	[1]	437,009	[1]	373,230	[1]
Cost of revenues:
Electricity	67,284	61,466	57,953	57,931	57,947	57,941	62,212	65,937	244,634		244,037		242,326
Product	26,771	42,130	31,818	34,627	32,796	17,137	9,249	16,890	135,346		76,072		53,277
Total cost of revenues	94,055	103,596	89,771	92,558	90,743	75,078	71,461	82,827	379,980		320,109		295,603
Gross margin	22,027	32,541	40,066	39,794	32,991	35,763	33,153	14,993	134,428		116,900		77,627
Operating expenses:
Research and development expenses	2,160	1,436	1,464	1,048	1,673	2,346	2,575	2,207	6,108		8,801		10,120
Selling and marketing expenses	3,089	3,445	4,666	4,922	6,882	2,940	3,725	2,660	16,122		16,207		13,447
General and administrative expenses	7,952	6,208	6,793	7,314	7,130	6,269	7,479	7,007	28,267		27,885		27,442
Impairment charges	229,113	7,264							236,377
Write-off of unsuccessful exploration activities	720		1,151	768					2,639				3,050
Operating income (loss)	(221,007)	14,188	25,992	25,742	17,306	24,208	19,374	3,119	(155,085)		64,007		23,568
Other income (expense):
Interest income	197	280	336	388	138	438	716	135	1,201		1,427		343
Interest expense, net	(19,528)	(15,400)	(14,263)	(14,878)	(15,028)	(23,909)	(17,442)	(13,080)	(64,069)		(69,459)		(40,473)
Foreign currency translation and transaction gains (losses)	1,369	615	(1,756)	14	196	(2,659)	596	517	242		(1,350)		1,557
Impairment of auction rate securities
Income attributable to sale of tax benefits	2,710	2,311	2,589	2,517	3,850	2,344	3,141	2,139	10,127		11,474		8,729
Other non-operating income (expense), net	246	215	290	(161)	206	347	915	(797)	590		671		130
Income (loss) from continuing operations, before income taxes and equity in income (losses) of investees	(236,013)	2,209	13,188	13,622	6,668	769	7,300	(7,967)	(206,994)		6,770		30,782
Income tax benefit (provision)	14,745	(1,479)	(4,309)	(5,457)	(49,261)	305	1,007	(586)	3,500		(48,535)		1,098
Equity in losses of investees	(980)	(1,245)	(157)	(140)	(407)	(71)	(69)	(412)	(2,522)		(959)		998
Net income (loss)	(222,248)	(515)	8,722	8,025	(43,000)	1,003	8,238	(8,965)	(206,016)		(42,724)		37,228
Net income attributable to noncontrolling interest	(136)	(67)	(81)	(130)	(80)	(137)	(105)	(10)	(414)		(332)		90
Net income (loss) attributable to the Company's stockholders	$ (222,384)	$ (582)	$ 8,641	$ 7,895	$ (43,080)	$ 866	$ 8,133	$ (8,975)	$ (206,430)		$ (43,056)		$ 37,318
Earnings (loss) per share attributable to the Company's stockholders - basic and diluted	$ (4.89)	$ (0.01)	$ 0.19	$ 0.17	$ (0.95)	$ 0.02	$ 0.18	$ (0.20)
Weighted average number of shares used in computation of earnings (loss) per share attributable to the Company's stockholders:
Basic	45,431	45,431	45,431	45,431	45,431	45,431	45,431	45,431	45,431		45,431		45,431
Diluted	45,431	45,431	45,438	45,437	45,431	45,440	45,443	45,431	45,431		45,431		45,452

[1] Revenues as reported in the geographic area in which they originate.