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Long-Term Debt, Net - Additional Information (Details) - USD ($)		1 Months Ended			12 Months Ended
	May 09, 2019	Jun. 30, 2018	Jul. 31, 2017	Jun. 30, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Jun. 25, 2018	Oct. 30, 2017	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Debt converted to shares issued					$ 0	$ 8,054,000	$ 0
Debt extinguishment costs					(152,000)	0	0
Debt issuance costs					1,245,000	1,170,000
Amortization of deferred debt issuance costs					$ 721,000	1,072,000	453,000
2019 Senior Secured Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Revolving line of credit borrowing capacity	$ 300,000,000
Line if Credit, Optional Addition to Borrowing Capacity	50,000,000
Unused commitment fee (percent)					0.30%
Remaining borrowing capacity					$ 158,856,000
Debt covenant, equity repurchase limit from employees, directors, officers or consultants	$ 3,000,000
2019 Senior Secured Credit Facility \| Line of Credit \| Minimum
Debt Instrument [Line Items]
Unused commitment fee (percent)	0.15%
2019 Senior Secured Credit Facility \| Line of Credit \| Maximum
Debt Instrument [Line Items]
Unused commitment fee (percent)	0.30%
2019 Senior Secured Credit Facility \| Line of Credit \| One, Two, Three or Six-Month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)					3.25%
2019 Senior Secured Credit Facility \| Line of Credit \| One, Two, Three or Six-Month LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	2.25%
2019 Senior Secured Credit Facility \| Line of Credit \| One, Two, Three or Six-Month LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	3.25%
2019 Senior Secured Credit Facility \| Line of Credit \| Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.50%
2019 Senior Secured Credit Facility \| Line of Credit \| LIBOR Plus 1%
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.00%				1.25%
2019 Senior Secured Credit Facility \| Line of Credit \| LIBOR Plus 1% \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.25%
2019 Senior Secured Credit Facility \| Line of Credit \| LIBOR Plus 1% \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.25%
2019 Senior Secured Credit Facility \| Line of Credit \| Letter of Credit \| Maximum
Debt Instrument [Line Items]
Unused commitment fee (percent)	3.25%
Term loans to bank under the Senior Secured Credit Facility \| Secured Debt
Debt Instrument [Line Items]
Original principal amount									$ 40,000,000
Long-term debt					$ 0	$ 35,000,000
Senior Secured Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Revolving line of credit borrowing capacity									$ 110,000,000
Quarterly principal payment					$ 1,250,000
Senior Secured Credit Facility \| Line of Credit \| Minimum
Debt Instrument [Line Items]
Unused commitment fee (percent)					0.15%
Senior Secured Credit Facility \| Line of Credit \| Maximum
Debt Instrument [Line Items]
Unused commitment fee (percent)					0.30%
Senior Secured Credit Facility \| Line of Credit \| Prime Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)					0.50%
Senior Secured Credit Facility \| Line of Credit \| Prime Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)					2.00%
Senior Secured Credit Facility \| Line of Credit \| 30-day LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)					2.75%
Senior Secured Credit Facility \| Line of Credit \| 30-day LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)					4.00%
Notes payable to Mezzanine Lenders \| Notes Payable
Debt Instrument [Line Items]
Original principal amount											$ 10,500,000
Stated interest rate (percent)											12.00%
Write off of unamortized debt issuance costs		$ 78,000
Warrants outstanding (shares)						1,423,688
Intrinsic value of warrants							$ 767,000	$ 9,241,000
Warrant exercise price (in USD per share)							$ 0.01
Junior Subordinated Notes \| Unsecured Debt
Debt Instrument [Line Items]
Original principal amount										$ 17,608,000
Stated interest rate (percent)										10.00%
Write off of unamortized debt issuance costs		43,000
Warrants outstanding (shares)										1,433,920
Debt repaid with proceeds from the Company's IPO		8,054,000
Common Stock \| Junior Subordinated Notes \| Unsecured Debt
Debt Instrument [Line Items]
Debt converted to shares issued			$ 500,000
Debt Conversion, Converted Instrument, Shares Issued			148,000
Debt extinguishment costs				$ 0
Class A Common Stock \| Common Stock
Debt Instrument [Line Items]
Debt converted to shares issued		$ 8,054,000