Income Taxes Computed at Federal Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Income Taxes [Line Items]
Income from continuing operations before taxes	$ (72,428)	$ (13,970)	$ 129,876	$ 26,913	$ (44,115)	$ (16,618)	$ 89,289	$ 32,843	$ 70,391	$ 61,399	$ 49,827
Provision for income taxes:
Tax at Federal statutory rate									24,637	21,490	17,440
Impact of Partnership loss not subject to federal income taxes									3,228	628	97
State taxes net of federal benefit									4,922	3,310	3,192
Permanent differences									78	57	37
Deferred tax benefit									(3,179)
Change in valuation allowance									3,027		(658)
Change in unrecognized tax benefit									81	(113)	55
Other									41	(57)	(242)
Income tax expense									$ 32,835	$ 25,315	$ 19,921