Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended				12 Months Ended			1 Months Ended		2 Months Ended	1 Months Ended
	Mar. 31, 2014	Oct. 31, 2013	May 31, 2013	Jul. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2010 warrant	Feb. 28, 2015	Feb. 28, 2015	Jan. 31, 2015
Class of Stock [Line Items]
Total shares reserved					9,154,740
Stock Issued During Period, Shares, New Issues	3,500,000		3,900,000	3,400,000
Share Price	$ 11.50		$ 4.14	$ 10.25
Exercise price of warrants					$ 12.25	$ 12.25
Shares of common stock to purchase by warrant					139,897	197,000
Payments of Stock Issuance Costs	$ 2,500,000		$ 39,000	$ 2,200,000
Proceeds from issuance of common stock, net of offering costs	37,800,000		16,100,000	32,300,000	37,754,000	20,988,000	32,306,000
Sales Agreement, Number of Shares Sold During Period		374,000
Sales Agreement, Average Share Price		$ 13.29
Sales Agreement, Net Proceeds		4,900,000			68,000	4,868,000
Sales Agreement, Termination Period					Apr. 01, 2014
Class of Warrant or Right, Exercise Price of Warrants or Rights, Weighted Average Price					25.06
Class of Warrant or Right, Outstanding					551,435
Warrant expiration date					Mar. 29, 2015
Fair Value Adjustment of Warrants					(863,000)	(41,000)	(511,000)
Class of Warrant or Right, Exercised During Period					57,581
Stock Issued During Period, Shares, Other					28,653
Proceeds from Warrant Exercises					68,857
Vulcan Incorporated
Class of Stock [Line Items]
Warrant expiration date								Oct. 21, 2015
Class of Warrant or Right, Number of Warrants Issued								3
Oxford
Class of Stock [Line Items]
Exercise price of warrants					$ 9.13
Shares of common stock to purchase by warrant					11,539
Warrant expiration date					Apr. 26, 2015
Shares from cash exercise of warrants [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, Other					5,621
Warrant 1 | Vulcan Incorporated
Class of Stock [Line Items]
Exercise price of warrants					$ 20.00			20
Shares of common stock to purchase by warrant					133,333			133,333
Warrant expiration date					Oct. 21, 2015
Warrant 2 | Vulcan Incorporated
Class of Stock [Line Items]
Exercise price of warrants					$ 30.00			30
Shares of common stock to purchase by warrant					133,333
Warrant expiration date					Oct. 21, 2015
Warrant 3 | Vulcan Incorporated
Class of Stock [Line Items]
Exercise price of warrants					$ 40.00			40
Shares of common stock to purchase by warrant					133,333
Options granted and outstanding
Class of Stock [Line Items]
Total shares reserved					8,364,469
Options available for future grant
Class of Stock [Line Items]
Total shares reserved					238,836
Common stock warrants
Class of Stock [Line Items]
Total shares reserved					551,435
Subsequent Event
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues									3,400,000
Share Price									$ 20.03	$ 20.03
Shares of common stock to purchase by warrant									749,250	749,250
Payments of Stock Issuance Costs									4,900,000
Proceeds from issuance of common stock, net of offering costs									79,100,000
Class of Warrant or Right, Outstanding									29,462	29,462
Stock Issued During Period, Shares, Other										104,741
Proceeds from Warrant Exercises										$ 1,300,000
Subsequent Event | Pre-funded warrants
Class of Stock [Line Items]
Share Price									$ 20.02	$ 20.02
Exercise price of warrants									$ 0.01	$ 0.01
Subsequent Event | Equity Incentive Plan 2008 | Equity Option [Member]
Class of Stock [Line Items]
Increase in authorized shares											1,709,273