Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Effective income tax rate	4.30%	(5.10%)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%
Income tax expense	$ 1.9	$ 6.0
Component of Income Tax Benefit Expense, Impairments, Nonrecurring [Member]
Income Taxes [Line Items]
Income tax expense		$ 12.3