Income Taxes - NOL and Capital Loss Carryforwards (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income tax
Income tax expense (benefit)	$ (96,800)	$ 22,756	$ (94,458)	$ 3,574
Effective income tax rate (as a percent)		31.00%		18.00%
Change in deferred tax valuation allowance		$ 208	(109,277)	$ (7,994)
Cumulative period of income		3 years
Valuation allowance	10,146	$ 10,354	10,146
Net operating and capital loss carryforwards	67,505	43,038	67,505
Tax credit carryforwards	$ 24,954	$ 27,406	$ 24,954
Minimum
Income tax
Carryover period for deferred tax attributes		20 years
Operating loss carryforwards expiration date		Sep. 30, 2017
Tax credit carryforwards, expiration date		Sep. 30, 2025
Maximum
Income tax
Operating loss carryforwards expiration date		Sep. 30, 2036
Tax credit carryforwards, expiration date		Sep. 30, 2036