CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (55,652,000)	$ (50,358,000)	$ (35,362,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	4,898,000	6,702,000	6,207,000
Depreciation and amortization	1,535,000	1,041,000	986,000
Loss on disposal of property and equipment	14,000	2,000	4,000
Changes in operating assets and liabilities:
Trade and other receivables, net	954,000	(2,481,000)	330,000
Inventories	(8,832,000)	(1,824,000)	(1,191,000)
Prepaid expenses and other current assets, net	4,000	64,000	(710,000)
Restricted cash	(600,000)	0	0
Other non-current assets	(325,000)	12,000	(94,000)
Accounts payable	(3,521,000)	3,278,000	(391,000)
Accrued clinical trial and related fees	3,684,000	(523,000)	3,503,000
Accrued payroll and related costs	1,215,000	769,000	255,000
Deferred revenue	3,400,000	1,097,000	1,070,000
Customer deposits	12,849,000	5,603,000	(2,299,000)
Other accrued expenses and current liabilities	1,051,000	(52,000)	(464,000)
Deferred rent, less current portion	(265,000)	651,000	(98,000)
Net cash used in operating activities	(39,591,000)	(36,019,000)	(28,254,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment acquisitions	(9,324,000)	(9,047,000)	(755,000)
Decrease (Increase) in other assets	533,000	598,000	(1,767,000)
Net cash used in investing activities	(8,791,000)	(8,449,000)	(2,522,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs of $677,000, $513,000 and $1,504,000, respectively	45,195,000	19,235,000	53,920,000
Proceeds from issuance of Series E preferred stock, net of issuance costs of $1,000, $1,002,000 and $1,458,000, respectively	59,000	18,203,000	17,917,000
Proceeds from issuance of common stock under Employee Stock Purchase Plan	540,000	608,000	545,000
Proceeds from exercise of stock options	138,000	298,000	944,000
Dividends paid on preferred stock	(4,139,000)	(3,352,000)	(232,000)
Principal payments on capital leases	0	(13,000)	(32,000)
Net cash provided by financing activities	41,793,000	34,979,000	73,062,000
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(6,589,000)	(9,489,000)	42,286,000
CASH AND CASH EQUIVALENTS, beginning of period	68,001,000	77,490,000	35,204,000
CASH AND CASH EQUIVALENTS, end of period	61,412,000	68,001,000	77,490,000
SUPPLEMENTAL INFORMATION:
Cash paid for interest	0	0	1,000
SCHEDULE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Accounts payable and other liabilities for purchase of property and equipment	1,565,000	4,673,000	4,000
Lease incentives	$ 562,000	$ 100,000	$ 0