Income Taxes Computed at Federal Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Taxes [Line Items]
Income from continuing operations before taxes	$ (29,092)	$ (21,766)	$ 66,996	$ 31,138	$ (31,923)	$ (4,993)	$ 94,113	$ 21,475	$ 47,276	$ 78,672	$ 70,391
Provision for income taxes:
Tax at Federal statutory rate									16,546	27,535	24,637
Impact of Partnership loss not subject to federal income taxes									741	477	3,228
State taxes net of federal benefit									3,170	5,672	4,922
Permanent differences									89	80	78
Deferred tax benefit											(3,179)
Change in valuation allowance									115	26	3,027
Change in unrecognized tax benefit											81
Other									(285)	(52)	41
Income tax expense									$ 20,376	$ 33,738	$ 32,835