Income Taxes Computed at Federal Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income from continuing operations before taxes	$ (32,629)	$ (15,963)	$ 117,316	$ 52,688	$ (44,051)	$ (2,051)	$ 83,108	$ 39,537	$ 121,412	$ 76,543	$ 25,154
Provision for income taxes:
Tax at Federal statutory rate									25,496	16,074	5,282
State taxes net of federal benefit									7,927	5,224	1,626
Permanent differences									196	89	345
Change in valuation allowance									86	(113)	23
Other									(30)	(649)	241
Income tax expense									$ 33,675	$ 20,625	$ 7,517