Net Loss Per Common Share (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2013

Dec. 31, 2012

Net Loss Per Common Share

Schedule of computation of basic and diluted net loss per share

	Nine months ended September 30,
	2013			2012
Basic and diluted net loss per common share calculation:
Net loss	$	(30,757	)	$	(10,731	)
Accretion of preferred stock dividends		(5,891	)		(5,288	)
Net loss attributable to common shareholders	$	(36,648	)	$	(16,019	)
Weighted average common shares outstanding		1,579			1,447
Net loss per share of common stock—basic and diluted	$	(23.21	)	$	(11.07	)

	Year Ended December 31,
	2012			2011
Basic and diluted net loss per common share calculation:
Net loss	$	(14,562	)	$	(18,633	)
Accretion of preferred stock dividends		(7,063	)		(6,838	)
Net loss attributable to common shareholders	$	(21,625	)	$	(25,471	)
Weighted average common shares outstanding		1,452			1,394
Net loss per share of common stock—basic and diluted	$	(14.89	)	$	(18.27	)

Schedule of potentially dilutive securities that have been excluded from the computations of diluted weighted average shares outstanding

	As of September 30,
	2013		2012
Redeemable convertible preferred stock		—		16,513
Options outstanding		2,620		1,301
Warrants		101		78
Total		2,721		17,892

	Year Ended December 31,
	2012		2011
Redeemable convertible preferred stock		16,663		16,064
Unvested restricted stock		—		18
Options outstanding		1,344		1,113
Warrants		95		38
Total		18,102		17,233