Warrants to Purchase Preferred Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended		6 Months Ended
	Jul. 02, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Warrants to Purchase Preferred Stock
Warrants Outstanding (in shares)		140,933		140,933
Fair Value		$ 926		$ 926		$ 1,103
Mark-to-market income related to the fair value measurement of the warrants		172	8	177	14
Number of warrants to purchase common stock, issued on conversion of warrants to purchase mandatorily redeemable convertible preferred stock	142,534
Series A
Warrants to Purchase Preferred Stock
Exercise Price (in dollars per share)		$ 1.27		$ 1.27
Warrants Outstanding (in shares)		35,520		35,520
Fair Value		277		277		299
Series B-1
Warrants to Purchase Preferred Stock
Exercise Price (in dollars per share)		$ 4.86		$ 4.86
Warrants Outstanding (in shares)		33,930		33,930
Fair Value		198		198		246
Series C
Warrants to Purchase Preferred Stock
Exercise Price (in dollars per share)		$ 3.79		$ 3.79
Warrants Outstanding (in shares)		31,659		31,659
Fair Value		208		208		245
Series 1
Warrants to Purchase Preferred Stock
Exercise Price (in dollars per share)		$ 2.46		$ 2.46
Warrants Outstanding (in shares)		31,130		31,130
Fair Value		211		211		256
Series 3
Warrants to Purchase Preferred Stock
Exercise Price (in dollars per share)		$ 5.75		$ 5.75
Warrants Outstanding (in shares)		8,694		8,694
Fair Value		$ 32		$ 32		$ 57