Subsequent Events - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 28, 2013 Subsequent Event IPO	Feb. 28, 2013 Subsequent Event IPO Common Stock	Feb. 28, 2013 Subsequent Event IPO Series C Convertible Preferred Stock	Feb. 28, 2013 Subsequent Event IPO Series D Convertible Preferred Stock	Feb. 28, 2013 Subsequent Event IPO Series E Convertible Preferred Stock
Subsequent Event [Line Items]
Common stock share issued				8,750,000
Public offering price for common stock				$ 8.00
Proceeds from issuance of common stock	$ 84,000	$ 34,000	$ 119,000	$ 70,000,000
Net proceed from issuance of common stock				61,500,000
Underwriting expenses				8,500,000
Underwriting discounts and commissions				4,900,000
Other offering expenses				$ 3,600,000
Conversion ratio of each preferred stock in to common stock						1.09	1.14	1.15
Preferred Stock available for conversion				12,329,330
Common stock available under initial public					13,210,843