Share-based compensation - Additional Information (Detail) (USD $)	12 Months Ended								0 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Maximum	Dec. 31, 2013 Minimum	Dec. 31, 2013 Stock Option Plan	Dec. 31, 2012 Stock Option Plan	Dec. 31, 2013 2004 Stock Incentive Plan	Dec. 31, 2013 2008 Stock Incentive Plan	Sep. 10, 2004 2004 Stock Incentive Plan	Sep. 10, 2004 2004 Stock Incentive Plan Maximum	Sep. 10, 2004 2004 Stock Incentive Plan Minimum	Aug. 27, 2008 2008 Stock Incentive Plan	Aug. 27, 2008 2008 Stock Incentive Plan Maximum	Aug. 27, 2008 2008 Stock Incentive Plan Minimum	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	$ 122,000	$ 134,000
Issuance of stock option to purchase stock	5,500,000
Common stock reserved for issuance	2,636,470								2,500,000			3,000,000			2,000,000	725,000
Share-based compensation arrangement by share based payment award options granted contractual term			10 years	5 years
Stock option awards vesting period			2 years
Options granted	173,354	30,843			173,354	30,843
Unrecognized compensation cost related to bon-vested	83,000
Plan expiration date									Sep. 10, 2014			Aug. 27, 2018			Jun. 11, 2007	Nov. 01, 2004
Options grant, expiration period										10 years	5 years		10 years	5 years
Intrinsic value of options exercised		$ 267,000
Share based compensation arrangement by share based payment award options grants in period gross							10,000	50,000