Borrowings - Narrative (Details)	Jul. 30, 2016	Dec. 31, 2018 USD ($) lender	Sep. 30, 2018 USD ($)	May 31, 2018 USD ($)	Jan. 31, 2010 USD ($)
Line of Credit Facility [Abstract]
Amount of available borrowings under the Secured Revolving Credit Facility		$ 183,500,000	$ 200,000,000
Senior Notes [Abstract]
Ownership interest In guarantor subsidiaries		100.00%
Secured Debt [Abstract]
Total debt, net		$ 1,255,784,000	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		36,253,000	36,770,000
Secured Debt [Abstract]
Total debt, net		$ 64,520,000	64,003,000
Weighted average fixed interest rate of debt (percent)		4.97%
Other secured notes payable
Secured Debt [Abstract]
Total debt, net		$ 2,634,000	4,113,000
Weighted average fixed interest rate of debt (percent)		1.88%
Revolving Credit Facility
Line of Credit Facility [Abstract]
Credit facility borrowing capacity		$ 210,000,000.0	200,000,000.0
Inventory assets pledged as collateral		$ 800,000,000
Number of lenders | lender		3
Borrowings outstanding		$ 25,000,000	0
Letters of credit secured using cash collateral		$ 1,500,000.0	0
Revolving Credit Facility | Maximum
Line of Credit Facility [Abstract]
Aggregate collateral ratio		4.00
Revolving Credit Facility | Minimum
Line of Credit Facility [Abstract]
Aggregate collateral ratio		1.00
Letter of Credit, Cash Secured
Line of Credit Facility [Abstract]
Letters of credit secured using cash collateral		$ 11,200,000	$ 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		$ 28,500,000
Standby Letters of Credit | Backstop Standby Letters of Credit
Line of Credit Facility [Abstract]
Credit facility borrowing capacity				$ 30,000,000