Borrowings - Narrative (Details)		3 Months Ended		6 Months Ended
	Jul. 30, 2016	Mar. 31, 2019 USD ($) lender	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) lender	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	May 31, 2018 USD ($)	Jan. 31, 2010 USD ($)
Line of Credit Facility [Abstract]
Amount of available borrowings under the Secured Revolving Credit Facility		$ 135,000,000		$ 135,000,000		$ 200,000,000
Senior Notes [Abstract]
Ownership interest In guarantor subsidiaries		100.00%		100.00%
Gain (loss) on extinguishment of debt		$ 216,000	$ 0	$ 216,000	$ (25,904,000)
Secured Debt [Abstract]
Total debt, net		1,301,760,000		1,301,760,000		1,231,254,000
Junior Subordinated Notes
Junior Subordinated Notes [Abstract]
Stated interest rate on debt instrument (percent)	7.987%
Effective period of debt instrument interest rate	10 years
Face amount modification								$ 75,000,000
Unamortized accretion		35,737,000		35,737,000		36,770,000
Secured Debt [Abstract]
Total debt, net		$ 65,037,000		$ 65,037,000		64,003,000
Weighted average fixed interest rate of debt (percent)		5.20%		5.20%
Other secured notes payable
Secured Debt [Abstract]
Total debt, net		$ 2,622,000		$ 2,622,000		4,113,000
Weighted average fixed interest rate of debt (percent)		1.88%		1.88%
Revolving Credit Facility
Line of Credit Facility [Abstract]
Credit facility borrowing capacity		$ 210,000,000.0		$ 210,000,000.0		200,000,000.0
Inventory assets pledged as collateral		$ 840,000,000		$ 840,000,000
Number of lenders | lender		3		3
Borrowings outstanding		$ 75,000,000		$ 75,000,000		0
Letters of credit secured using cash collateral		$ 0		$ 0		0
Revolving Credit Facility | Maximum
Line of Credit Facility [Abstract]
Aggregate collateral ratio		4.00		4.00
Revolving Credit Facility | Minimum
Line of Credit Facility [Abstract]
Aggregate collateral ratio		1.00		1.00
Letter of Credit, Cash Secured
Line of Credit Facility [Abstract]
Letters of credit secured using cash collateral		$ 10,900,000		$ 10,900,000		$ 10,400,000
Standby Letters of Credit | Standby Letters for Credit Facility
Line of Credit Facility [Abstract]
Credit facility borrowing capacity							$ 50,000,000.0
Letters of credit secured using cash collateral		36,300,000		$ 36,300,000
Standby Letters of Credit | Backstop Standby Letters of Credit
Line of Credit Facility [Abstract]
Credit facility borrowing capacity							$ 40,000,000
Senior Notes
Senior Notes [Abstract]
Gain (loss) on extinguishment of debt		200,000
Non-cash (gain) loss on extinguishment of debt		100,000
Senior Notes | Unsecured Senior Notes 7.25 Percent
Senior Notes [Abstract]
Extinguishment of debt, amount		1,200,000
Senior Notes | Unsecured Senior Notes 6.75 Percent
Senior Notes [Abstract]
Extinguishment of debt, amount		$ 3,800,000