REVENUE - Impact of Adopting ASC 606 on Unaudited Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (882)	$ (662)	$ (2,438)	$ (2,692)	$ (1,462)	$ (1,433)	$ (3,669)	$ (6,564)	$ (6,674)	$ (13,128)	$ (12,288)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation									1,339	1,404	1,451
Amortization of intangible assets									444	607	881
Stock-based compensation									825	1,102	1,605
Amortization of debt issue costs									101	92	110
Provision for inventory reserves									(202)	1,261	2,212
Provision for bad debts									56	22	132
Other									57	(94)	178
Changes in operating assets and liabilities:
Accounts receivable									(5,840)	419	1,687
Revenue earned but not billed									(1,390)
Inventories									(4,689)	4,706	1,220
Deferred contract costs									0	(65)	(899)
Prepaid expenses and other current assets									68	391	1,974
Accounts payable									8,916	20	(81)
Accrued expenses and other									1,975	(1,736)	(635)
Deferred revenue, current and long-term									(44)	(126)	300
Net cash used in operating activities									(5,058)	(4,415)	(1,903)
Investing activities
Purchase of property and equipment									(381)	(512)	(660)
Additions to patents and licenses									(68)	(73)	(291)
Net cash (used in) provided by investing activities									(449)	(585)	1,649
Financing activities
Payment of long-term debt									(80)	(158)	(880)
Proceeds from revolving credit facility									60,270	68,734	87,935
Payment of revolving credit facility									(54,976)	(71,456)	(85,025)
Payments to settle employee tax withholdings on stock-based compensation									(10)	(9)	(19)
Debt issue costs									(396)
Net proceeds from employee equity exercises									4	6	8
Net cash provided by (used in) financing activities									4,812	(2,883)	2,019
Net (decrease) increase in cash and cash equivalents									(695)	(7,883)	1,765
Cash and cash equivalents at beginning of period				9,424				$ 17,307	9,424	17,307	15,542
Cash and cash equivalents at end of period	8,729				9,424				8,729	9,424	$ 17,307
ASC 606 | Adjustments
Operating activities
Net loss									79
Changes in operating assets and liabilities:
Accounts receivable									(217)
Revenue earned but not billed									1,390
Inventories									(335)
Deferred contract costs									599
Prepaid expenses and other current assets									(1,512)
Accounts payable									102
Accrued expenses and other									84
Deferred revenue, current and long-term									(190)
ASC 606 | Balances without application of ASC 606
Operating activities
Net loss									(6,595)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation									1,339
Amortization of intangible assets									444
Stock-based compensation									825
Amortization of debt issue costs									101
Provision for inventory reserves									(202)
Provision for bad debts									56
Other									57
Changes in operating assets and liabilities:
Accounts receivable									(6,057)
Inventories									(5,024)
Deferred contract costs									599
Prepaid expenses and other current assets									(1,444)
Accounts payable									9,018
Accrued expenses and other									2,059
Deferred revenue, current and long-term									(234)
Net cash used in operating activities									(5,058)
Investing activities
Purchase of property and equipment									(381)
Additions to patents and licenses									(68)
Net cash (used in) provided by investing activities									(449)
Financing activities
Payment of long-term debt									(80)
Proceeds from revolving credit facility									60,270
Payment of revolving credit facility									(54,976)
Payments to settle employee tax withholdings on stock-based compensation									(10)
Debt issue costs									(396)
Net proceeds from employee equity exercises									4
Net cash provided by (used in) financing activities									4,812
Net (decrease) increase in cash and cash equivalents									(695)
Cash and cash equivalents at beginning of period				$ 9,424					9,424
Cash and cash equivalents at end of period	$ 8,729				$ 9,424				$ 8,729	$ 9,424