Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parentheical) (USD $)	1 Months Ended			12 Months Ended	1 Months Ended
	Oct. 31, 2012 Common Stock	Jan. 31, 2012 Common Stock	Jan. 31, 2010 Common Stock	Dec. 31, 2012 Common Stock	Nov. 30, 2010 Series C Redeemable Convertible Preferred Stock	Jul. 31, 2012 Series D Redeemable Convertible Preferred Stock	Aug. 31, 2011 Series D Redeemable Convertible Preferred Stock
Per share price of stock issued (in dollars per share)	$ 22.50	$ 8.22	$ 5.50	$ 16.00	$ 13.3530	$ 13.9040	$ 13.9040
Issuance costs				$ 8,481,000			$ 1,138,000
Issuance of common stock (in shares)				5,060,000