Net Income (Loss) Per Share - Components and Calculation of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income (loss)		$ (68,086)	$ (66,655)	$ (68,979)	$ 941
Dividends on preferred shares	[1]	6,000	6,000	12,000	6,000
Net income (loss) attributable to common shareholders		(74,086)	(72,655)	(80,979)	(5,059)
Net income (loss) attributable to common shareholders - basic and diluted		$ (74,086)	$ (72,655)	$ (80,979)	$ (5,059)
Weighted-average common shares outstanding - basic		68,451,920	68,019,300	68,348,850	67,922,276
Weighted-average common shares outstanding - diluted		68,451,920	68,019,300	68,348,850	67,922,276
Net income (loss) per share - basic	[2]	$ (1.08)	$ (1.07)	$ (1.18)	$ (0.07)
Net income (loss) per share - diluted	[2]	$ (1.08)	$ (1.07)	$ (1.18)	$ (0.07)

[1] Amounts for the three months ended March 31, 2019 and the three and six months ended March 31, 2018 are composed of $5.0 million in undeclared cumulative Preferred Stock dividends, as well as an additional $1.0 million of Preferred Stock dividends that had been declared and paid as of period end. Six months ended March 31, 2019 amount is composed of $5.0 million in undeclared cumulative Preferred Stock dividends, as well as an additional $7.0 million of Preferred Stock dividends that had been declared and paid as of period end. See Note 3 for further discussion.

[2] See Note 5 for detailed calculations and further discussion.