Consolidated Statements of Changes in Mandatorily Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Additional Paid-in Capital [Member]
Initial public offering, issuance cost	$ 4,413	$ 7,180
Series E Preferred Stock [Member]
Issuance of preferred stock, issuance costs			$ 185