Share-Based compensation - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended				1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Maximum	Dec. 31, 2012 Minimum	Sep. 10, 2004 Stock Incentive Plan 2004	Sep. 10, 2004 Stock Incentive Plan 2004 Maximum	Aug. 27, 2008 2008 Stock Incentive Plan	Aug. 27, 2008 2008 Stock Incentive Plan Maximum	Sep. 10, 2004 2004 Stock Incentive Plan	Aug. 19, 1999 1997 Employee Stock Option Plan	Oct. 31, 1994 1994 Employee Stock Option Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share based compensation expense	$ 134,000	$ 69,000
Issuance of stock option to purchase stock	5,500,000
Common stock reserved for issuance	2,636,470						3,000,000		2,500,000	2,000,000	725,000
Stock option awards vesting period			2 years
Plan expiration date							Aug. 27, 2018		Sep. 10, 2014	Jun. 11, 2007	Nov. 01, 2004
Options grant, expiration period, years, maximum					5 years	10 years	5 years	10 years
Intrinsic value of options exercised		$ 1,000
Share-based compensation arrangement by sharebased payment award options graned contractual term			10 years	5 years