Regulatory matters and revenues subject to refund (Details) (USD $) In Millions, unless otherwise specified	Dec. 21, 2012	Sep. 26, 2012
Regulatory Assets [Line Items]
Total gas rate increase requested	$ 1.5	$ 3.5
Percent above current rates requested	3.30%	5.90%
Amount of requested interim increase in annual gas rates		$ 1.7
Requested percentage of interim gas rate increase		2.90%