Regulatory Matters - Summary of Utilities Rate Plans (Pike County Light & Power Company (Pike)-Electric) (Detail) (Pike County Light & Power Company (Pike) [Member], Electric Transmission [Member], USD $)	12 Months Ended	60 Months Ended	12 Months Ended	60 Months Ended
	Mar. 31, 2010	Mar. 31, 2014	Aug. 31, 2015	Aug. 31, 2015
Public Utilities, General Disclosures [Line Items]
Base rate changes	$ 900,000
Amortization to income of net regulatory (assets) and liabilities		100,000
Scenario, Forecast [Member]
Public Utilities, General Disclosures [Line Items]
Base rate changes			1,250,000
Amortization to income of net regulatory (assets) and liabilities				$ (70,000)