Regulatory Matters (Details 2) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Regulatory Assets
Deferred construction accounting costs	$ 16,964	$ 10,521
Iatan1
Regulatory Assets
Deferred construction accounting costs	5,796	5,849
Iatan1 | Deferred Carrying Charges
Regulatory Assets
Deferred construction accounting costs	2,753	2,779
Iatan1 | Deferred O&M
Regulatory Assets
Deferred construction accounting costs	1,376	1,388
Iatan1 | Depreciation
Regulatory Assets
Deferred construction accounting costs	1,667	1,682
Iatan2
Regulatory Assets
Deferred construction accounting costs	10,817	4,524
Iatan2 | Deferred Carrying Charges
Regulatory Assets
Deferred construction accounting costs	3,925	1,770
Iatan2 | Deferred O&M
Regulatory Assets
Deferred construction accounting costs	4,244	1,643
Iatan2 | Depreciation
Regulatory Assets
Deferred construction accounting costs	2,648	1,111
Plum point
Regulatory Assets
Deferred construction accounting costs	351	148
Plum point | Deferred Carrying Charges
Regulatory Assets
Deferred construction accounting costs	66	33
Plum point | Deferred O&M
Regulatory Assets
Deferred construction accounting costs	173	70
Plum point | Depreciation
Regulatory Assets
Deferred construction accounting costs	$ 112	$ 45