Stockholders' Equity - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended		3 Months Ended		12 Months Ended	1 Months Ended
	Aug. 02, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Nov. 30, 2013	Dec. 31, 2014	Feb. 27, 2015	May 31, 2008	Aug. 31, 2013	Jan. 31, 2012	Jul. 17, 2013
Class Of Stock [Line Items]
Shares authorized under shelf registration statement		150,000,000	150,000,000
Issuance of common stock		81,536,724	78,113,639
Offering price per share	$ 4.50
Proceeds from issuance of common stock	$ 43,400,000
Underwriting discounts and commissions and other offering expenses	3,200,000
Issuance of common stock from stock options exercises, net, Shares		205,033	183,796
Issuance of common stock from warrant exercises, net, Shares		210,600	2,713,207
Warrants exercised		211,647	3,201,633
Stock option exercised		205,684	183,796
Restricted stock awards issued to member of senior management		200,000
Research and development expense [Member]
Class Of Stock [Line Items]
Total employee stock-based compensation recorded as operating expenses		15,000	16,000	4,000	0	23,000
General and administrative expense [Member]
Class Of Stock [Line Items]
Total employee stock-based compensation recorded as operating expenses		406,000	801,000	474,000	0	812,000
Restricted stock [Member]
Class Of Stock [Line Items]
Restricted stock awards vested during the period		262,245	472,247	221,302		1,233,409
Restricted stock surrendered				24,690		89,674
Common stock returned by holders				10,000		95,842
Restricted stock awards granted		0	60,000	55,000		1,380,000
Total employee stock-based compensation recorded as operating expenses		421,000	817,000	478,000	0	835,000
Unrecognized restricted stock-based compensation expense		222,000
Total unrecognized compensation cost related, weighted average period		7 months 13 days
Restricted stock units (RSUs) [Member]
Class Of Stock [Line Items]
Restricted stock awards vested during the period		255,000	405,000	50,000		211,250
Restricted stock surrendered		137,816	218,655
Stock option granted with immediate vesting		137,816	218,655	24,690		89,674
Percentage of vesting schedule						25.00%
Period for vesting schedule over start date						4 years
Senior Management [Member]
Class Of Stock [Line Items]
Restricted stock awards vested during the period		150,000
Restricted stock surrendered		50,000
Senior Management [Member] | Restricted stock units (RSUs) [Member]
Class Of Stock [Line Items]
Restricted stock awards granted						950,000
Non-Executive Employees [Member] | Restricted stock units (RSUs) [Member]
Class Of Stock [Line Items]
Restricted stock awards granted						130,000
Consultants [Member] | Restricted stock units (RSUs) [Member]
Class Of Stock [Line Items]
Restricted stock awards granted			60,000	55,000		100,000
Percentage of vesting schedule						100.00%
Period for vesting schedule over start date						6 months
Equity Distribution Agreement [Member]
Class Of Stock [Line Items]
Value of shares sold under equity distribution agreement		16,100,000	3,500,000
Issuance of common stock from stock options exercises, net, Shares		2,197,768	334,412
Equity Offering Sales Agreement [Member]
Class Of Stock [Line Items]
Value of shares sold under equity distribution agreement		6,200,000
Issuance of common stock from stock options exercises, net, Shares		1,000,000
Maximum [Member] | Equity Distribution Agreement [Member]
Class Of Stock [Line Items]
Number of shares to be offered and sold in equity distribution agreement							4,000,000
Securities authorized for offer and sale, amount								26,777,785
Underwriting Agreement [Member]
Class Of Stock [Line Items]
Securities authorized for offer and sale, amount									$ 190,000,000
Equity Incentive Plan 2008 [Member]
Class Of Stock [Line Items]
Common shares authorized to be issued										1,521,584
Termination date of Equity Incentive Plan		Jul. 01, 2018
Shares issued during the year		0
Equity Incentive Plan 2012 [Member]
Class Of Stock [Line Items]
Common shares authorized to be issued											5,000,000	6,553,986
Shares available for issuance											11,553,986
Termination period of Equity Incentive Plan		10 years
IPO [Member]
Class Of Stock [Line Items]
Shares authorized under shelf registration statement													100,000,000
Issuance of common stock	10,350,000
Offering price per share	$ 4.23
Overallotment Option Exercised [Member] | Underwriting Agreement [Member]
Class Of Stock [Line Items]
Issuance of common stock	1,350,000