Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2013

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

The compensation expense related to the Company’s stock-based compensation arrangements has been included in the condensed statements of operations and comprehensive loss as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2013		2012		2013		2012
General and administrative	$	7,316	$	626	$	9,504	$	1,876
Research and development		313		2,500		4,377		7,502
Total share-based compensation expense	$	7,629	$	3,126	$	13,881	$	9,378

Summary of Estimated Fair Value of Stock Option Granted

The estimated fair value of each stock option granted was determined on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions for the stock option grants:

	Three and Nine Months Ended September 30,
	2013			2012
Risk-free interest rate		1.75	%		—
Expected volatility of common stock		71	%		—
Dividend yield		0.0	%		—
Expected option term		6 years			—