UNAUDITED QUARTERLY DATA - Summary of Impact on Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and cash equivalents	$ 27,464		$ 83,964	$ 17,055	$ 15,360	$ 51,870	$ 12,745	$ 17,780	$ 18,034	$ 18,198
Accounts receivable	21,712		15,748	19,443	14,707	9,815	6,834	6,662	6,892	5,607
Finance receivables, net	6,260		4,603	2,234	3,296	1,441	9,743	2,149	1,442	3,349
Inventory, net	10,908		8,038	11,923	12,019	8,876	5,192	3,677	4,438	3,926
Prepaid expenses and other current assets	1,558	$ 1,180	929	1,278	1,610	1,056	879	1,594	1,677	1,352
Other assets	2,099	1,974	720	414	458	289	319	231	144	163
Goodwill	64,149		64,149	64,149	64,403	11,492	11,492	11,492	11,492	11,703
Property and equipment, net	9,180		11,273	12,243	12,443	10,701	11,111	11,341	11,994	12,436
Accounts payable	27,511		30,468	29,574	23,908	14,506	16,345	11,819	9,109	8,710
Accrued expenses	23,258		19,291	18,508	16,623	12,217	11,873	8,792	7,541	8,135
Line of credit, net						7,051	7,036	7,034	7,091	7,271
Capital lease obligations and current obligations under long-term debt	12,497		34,639	4,470	5,488	2,628	3,198	3,785	4,331	4,952
Deferred revenue	1,539	$ 1,638	511	511	730	439	268	310	478	94
Deferred gain from sale-leaseback transactions				0	0	0	0	0	0	0
Deferred gain from sale-leaseback transactions, less current portion					0	0	0
Capital lease obligations and long-term debt, less current portion	276		1,127	22,895	24,570	1,049	1,061	1,239	1,394	1,517
Common stock	$ 376,853		$ 375,436	310,522	310,150	286,296	245,999	245,463	245,230	244,996
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and cash equivalents				(52)	(26)	0	0	0	0	0
Accounts receivable				(3,723)	(765)	(473)	(359)	(72)	96	(233)
Finance receivables, net				(1,670)	(2,221)	(1,641)	(1,267)	92	0	0
Inventory, net				893	804	636	606	(470)	(348)	(338)
Prepaid expenses and other current assets				(591)	(361)	(66)	(89)	(34)	(87)	(87)
Other assets				(800)	(662)	(461)	(368)	94	(1)	0
Goodwill				(47)	(46)	0	0	0	0	0
Property and equipment, net				45	(179)	(1,149)	(1,000)	2,168	2,561	2,866
Accounts payable				128	133	295	291	290	19	17
Accrued expenses				10,547	9,825	8,422	7,743	5,681	4,629	4,223
Line of credit, net						0	0	13	13	13
Capital lease obligations and current obligations under long-term debt				(5)	367	(21)	(32)	2,999	3,565	4,118
Deferred revenue				70	135	439	268	310	478	94
Deferred gain from sale-leaseback transactions				(198)	(198)	(197)	(239)	(255)	(470)	(685)
Deferred gain from sale-leaseback transactions, less current portion					(49)	(99)	(100)
Capital lease obligations and long-term debt, less current portion				0	696	0	0	0	0	0
Common stock				2,888	3,097	(167)	0	0	0	0
Adjustments | Customer Transaction Investigation-related Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts receivable				(1,954)	(1,774)	(315)		0	0	0
Finance receivables, net				(1,666)	(1,269)	(1,640)		92	0	0
Inventory, net				2,459	2,166	941		0	0	0
Prepaid expenses and other current assets				25	25	25		30	0	0
Other assets				69	76	82		95	0	0
Property and equipment, net				(146)	(162)	0		0	0	0
Accounts payable				99	106	270		270	0	0
Accrued expenses				341	580	803		34	0	0
Adjustments | Acquisition Integration-related Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cash and cash equivalents				(52)	(26)	0		0	0	0
Accounts receivable				(1,974)	1,133	0		0	0	0
Finance receivables, net				158	(1,515)	0		0	0	0
Inventory, net				(500)	(500)	0		0	0	0
Prepaid expenses and other current assets				(44)	(35)	0		0	0	0
Other assets				(175)	(139)	0		0	0	0
Goodwill				4,121	4,121	0		0	0	0
Property and equipment, net				826	721	0		0	0	0
Accrued expenses				883	785	0		0	0	0
Deferred revenue				(153)	(153)	0		0	0	0
Common stock				3,469	3,469	0		0	0	0
Adjustments | Significant Account and Transaction Review and Other
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts receivable				127	(8)	77	(75)	61	110	(143)
Finance receivables, net				28	1,074	0		0	0	0
Inventory, net				(1,067)	(861)	(305)	(500)	(470)	(348)	(338)
Prepaid expenses and other current assets				(173)	(150)	(136)	(114)	13	13	13
Other assets				(693)	(600)	(543)	(456)	0	0	0
Property and equipment, net				(635)	(737)	(1,149)	(1,000)	2,168	2,561	2,865
Accounts payable				29	27	25	21	21	19	17
Accrued expenses				9,877	9,087	8,319	7,235	6,166	5,222	4,506
Line of credit, net				0	0	0		13	13	13
Capital lease obligations and current obligations under long-term debt				(5)	367	(21)	(32)	2,998	3,566	4,117
Deferred revenue				(27)	(27)	(27)	(27)	0	0	0
Deferred gain from sale-leaseback transactions				(198)	(198)	(198)	(239)	(255)	(470)	(685)
Deferred gain from sale-leaseback transactions, less current portion				0	(49)	(99)	$ (100)	0	0	0
Capital lease obligations and long-term debt, less current portion				0	697	0		0	0	0
Common stock				$ (867)	$ (372)	$ (166)		$ 0	$ 0	$ 0