Stock-based Compensation - Summary of Stock-Based Compensation Expense (Detail) (USD $)	3 Months Ended		9 Months Ended		80 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 7,629	$ 3,126	$ 13,881	$ 9,378	$ 103,592
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	7,316	626	9,504	1,876
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total share-based compensation expense	$ 313	$ 2,500	$ 4,377	$ 7,502