Financing Activities (Details) (USD $)	0 Months Ended	3 Months Ended								12 Months Ended			84 Months Ended	12 Months Ended			0 Months Ended		12 Months Ended	0 Months Ended							0 Months Ended		0 Months Ended			0 Months Ended			0 Months Ended			0 Months Ended		12 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 30, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012 Series A Warrant	Dec. 31, 2012 Series B Warrant	Jun. 18, 2007 Series A preferred shares Series A Warrant	Jan. 04, 2008 Series A-1 Preferred Stock License Agreements	Aug. 09, 2007 Series A-1 Preferred Stock License Agreements	Dec. 31, 2008 Series A-1 Preferred Stock License Agreements	Aug. 09, 2007 Junior Series A Preferred Stock Divestiture Agreement	Mar. 15, 2013 Series B Preferred Stock Series B Warrant	Dec. 24, 2012 Series B Preferred Stock Series B Warrant	Jun. 20, 2012 Series B Preferred Stock Series B Warrant	Apr. 14, 2008 Series A Investors Series A preferred shares	Aug. 09, 2007 Series A Investors Series A preferred shares	Aug. 09, 2007 Series A Investors Series A preferred shares Initial Closing	Aug. 09, 2007 Series A Investors Series A preferred shares First Milestone Event	Aug. 09, 2007 Series A Investors Series A preferred shares Initiation of Phase 1b study of assets acquired or licensed	Apr. 14, 2008 Series A Investors Series A preferred shares Second Milestone Event	Sep. 19, 2008 Series A Investors Series A preferred shares Third Milestone Event	Apr. 14, 2008 Series A Investors Series A preferred shares Third Milestone Event	May 06, 2009 Series A Investors Series A preferred shares Fourth and Fifth Milestone Event	Apr. 14, 2008 Series A Investors Series A preferred shares Fourth Milestone Event	Apr. 14, 2008 Series A Investors Series A preferred shares Fifth Milestone Event	Oct. 14, 2009 Series A Investors Series A preferred shares Additional closing	Dec. 11, 2009 Series B Investors Series B Preferred Stock	Dec. 11, 2009 Series B Investors Series B Preferred Stock Initial Closing	Mar. 01, 2011 Series B Investors Series B Preferred Stock Second Closing	Dec. 11, 2009 Series B Investors Series B Preferred Stock Second Closing	Dec. 31, 2013 Notes	Mar. 31, 2013 Notes	Dec. 31, 2012 Notes	Jun. 30, 2012 Notes	Jun. 18, 2007 Notes
Financing activities
Secured promissory notes issued																																									$ 1,500,000	$ 4,000,000	$ 7,500,000	$ 200,000
Interest rate (as a percent)																																								3.00%				8.00%
Share price (in dollars per share)																	$ 1.00	$ 1.00		$ 1.00				$ 1.00	$ 1.00					$ 1.00		$ 1.00			$ 1.00	$ 1.00		$ 1.00
Shares available for sale and issuance under agreement																										9,253,101	9,217,243	17,319,656	6,000,000		13,000,000		4,319,656	7,000,000			15,000,000		15,000,000
Period up to which the License Agreement is to be kept in effect																											10 days
Warrants issued (in shares)																210,000					35,700	95,200	225,000
Exercise price of warrants (in dollars per share)																$ 0.01					$ 2.50	$ 2.50	$ 1.00
Warrant Liability											966,000			500,000	400,000
Change in fair value of warrant liability														330,000	36,000
Shares issued	8,740,000																4,000,000	2,000,000		3,000,000									6,000,000	13,000,000		11,319,656			3,000,000			15,000,000
Proceeds from issuance of shares										49,699,000		14,990,000	130,632,000																	13,000,000		11,300,000
Extinguishment of liability due to exercise of investor rights																														300,000		300,000
Research and development expense		15,379,000	11,101,000	4,345,000	2,390,000	1,998,000	1,595,000	1,578,000	1,621,000	33,215,000	6,792,000	13,896,000	108,107,000						4,000,000
Basis of interest rate																																								LIBOR
Public offering price (in dollars per share)	$ 22.00
Fair value of warrant liability reclassified to additional paid-in capital	2,200,000		2,200,000
Charge related to change in fair value of warrant liability										$ 1,181,000	$ 366,000	$ 7,000	$ 1,563,000