Regulatory Matters (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Regulatory Assets
Deferred construction accounting costs	$ 17,087	$ 17,095
Iatan1
Regulatory Assets
Deferred construction accounting costs	5,718	5,743
Iatan1 | Deferred Carrying Charges
Regulatory Assets
Deferred construction accounting costs	2,715	2,728
Iatan1 | Deferred O&M
Regulatory Assets
Deferred construction accounting costs	1,358	1,363
Iatan1 | Depreciation.
Regulatory Assets
Deferred construction accounting costs	1,645	1,652
Iatan2
Regulatory Assets
Deferred construction accounting costs	10,870	10,890
Iatan2 | Deferred Carrying Charges
Regulatory Assets
Deferred construction accounting costs	3,873	3,891
Iatan2 | Deferred O&M
Regulatory Assets
Deferred construction accounting costs	4,279	4,271
Iatan2 | Depreciation.
Regulatory Assets
Deferred construction accounting costs	2,718	2,728
Plum point
Regulatory Assets
Deferred construction accounting costs	499	462
Plum point | Deferred Carrying Charges
Regulatory Assets
Deferred construction accounting costs	65	65
Plum point | Deferred O&M
Regulatory Assets
Deferred construction accounting costs	276	239
Plum point | Depreciation.
Regulatory Assets
Deferred construction accounting costs	$ 158	$ 158