Income Taxes Computed at Federal Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Taxes [Line Items]
Income from continuing operations before taxes	$ (31,923)	$ (4,993)	$ 94,113	$ 21,475	$ (72,428)	$ (13,970)	$ 129,876	$ 26,913	$ 78,672	$ 70,391	$ 61,399
Provision for income taxes:
Tax at Federal statutory rate									27,535	24,637	21,490
Impact of Partnership loss not subject to federal income taxes									477	3,228	628
State taxes net of federal benefit									5,672	4,922	3,310
Permanent differences									80	78	57
Deferred tax benefit										(3,179)
Change in valuation allowance									26	3,027
Change in unrecognized tax benefit										81	(113)
Other									(52)	41	(57)
Income tax expense									$ 33,738	$ 32,835	$ 25,315