Segment Information - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Mar. 31, 2016 Business Segment	Sep. 30, 2015 Segment
Segment Reporting Information [Line Items]
Number of primary businesses | Business	3
Number of reportable segments	7
Building Efficiency
Segment Reporting Information [Line Items]
Number of reportable segments	4	3