CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	9 Months Ended
	Jan. 31, 2016	Jan. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (43,768,000)	$ (38,223,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	3,740,000	5,280,000
Depreciation and amortization	921,000	803,000
Loss on disposal of property and equipment	14,000	1,000
Changes in operating assets and liabilities:
Trade and other receivables, net	(4,786,000)	(4,952,000)
Inventories	(7,835,000)	(618,000)
Prepaid expenses and other current assets, net	(991,000)	485,000
Other non-current assets	(211,000)	(1,000)
Accounts payable	(4,289,000)	1,870,000
Accrued clinical trial and related fees	3,065,000	(1,316,000)
Accrued payroll and related expenses	(109,000)	(121,000)
Deferred revenue	8,788,000	219,000
Customer deposits	11,070,000	2,551,000
Other accrued expenses and current liabilities	610,000	1,000
Deferred rent	(193,000)	410,000
Net cash used in operating activities	(33,974,000)	(33,611,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment acquisitions	(7,909,000)	(4,805,000)
Decrease in other assets	426,000	1,139,000
Net cash used in investing activities	(7,483,000)	(3,666,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs of $633,000 and $193,000, respectively	43,498,000	7,205,000
Proceeds from issuance of Series E preferred stock, net of issuance costs of $1,000 and $553,000, respectively	59,000	9,567,000
Proceeds from issuance of common stock under Employee Stock Purchase Plan	334,000	307,000
Proceeds from exercise of stock options, net of issuance costs of $1,000 and $3,000, respectively	138,000	277,000
Dividends paid on preferred stock	(3,103,000)	(2,318,000)
Principal payments on capital leases	0	(13,000)
Net cash provided by financing activities	40,926,000	15,025,000
NET DECREASE IN CASH AND CASH EQUIVALENTS	(531,000)	(22,252,000)
CASH AND CASH EQUIVALENTS, beginning of period	68,001,000	77,490,000
CASH AND CASH EQUIVALENTS, end of period	67,470,000	55,238,000
SCHEDULE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Accounts payable and other liabilities for purchase of property and equipment	1,748,000	2,510,000
Lease incentives	$ 0	$ 370,000