Earnings Per Share - Summary of Basic and Diluted EPS (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Preferred Stock Dividends, Income Statement Impact				$ (5.1)
Preferred Stock, Accretion of Redemption Discount				(24.3)
Preferred Stock Conversions, Inducements				29.3
Dilutive Adjustments To Income Loss Attributable To Common Stock From Assumed Conversion Of Preferred Stock Net Of Tax				0.1
Net income (loss) attributable to common and participating preferred stockholders	(87.6)	(45.5)	(126.6)	16.5
Participating shares at end of period:
Common shares outstanding	142,801	139,724	142,801	139,724
Preferred shares (as-converted basis)	59,134	62,839	59,134	62,839
Total	201,935	202,563	201,935	202,563
Percentage of income (loss) allocated to:
Common shares	100.00%	100.00%	100.00%	69.00%
Preferred shares (a)	0.00%	0.00%	0.00%	31.00%
Net income (loss) attributable to common shares - basic	(87.6)	(45.5)	(126.6)	11.4
Dilutive adjustments to income (loss) attributable to common shares from assumed conversion of preferred shares, net of tax:
Net income (loss) attributable to common shares - diluted	$ (87.6)	$ (45.5)	$ (126.6)	$ 11.5
Weighted-average common shares outstanding - basic	139,889	139,724	139,529	139,604
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock				62,839
Dilutive effect of unvested restricted stock and restricted stock units				1,856
Dilutive effect of stock options				592
Weighted-average shares outstanding - diluted	139,889	139,724	139,529	204,891
Net (loss) income per common share attributable to controlling interest:
Basic (in dollars per share)	$ (0.63)	$ (0.33)	$ (0.91)	$ 0.08
Diluted (in dollars per share)	$ (0.63)	$ (0.33)	$ (0.91)	$ 0.06