Share-based compensation - Additional Information (Detail) (USD $)	3 Months Ended					12 Months Ended	0 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Maximum	Mar. 31, 2014 Minimum	Mar. 31, 2014 Stock Option Plan	Dec. 31, 2013 Stock Option Plan	Sep. 10, 2004 2004 Stock Incentive Plan	Mar. 31, 2014 2004 Stock Incentive Plan	Mar. 31, 2014 2004 Stock Incentive Plan Maximum	Aug. 27, 2008 2008 Stock Incentive Plan	Mar. 31, 2014 2008 Stock Incentive Plan	Mar. 31, 2014 2008 Stock Incentive Plan Maximum	Aug. 19, 1999 1997 Employee Stock Option Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share based compensation expense	$ 9,000	$ 33,000
Issuance of stock option to purchase stock	5,500,000
Common stock reserved for issuance	2,521,733						2,500,000			3,000,000			2,000,000
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	0	50,000			0	173,354
Unrecognized compensation cost related to bon-vested	74,000
Plan expiration date							Sep. 10, 2014			Aug. 27, 2018			Jun. 11, 2007
Intrinsic value of options exercised	$ 2,816,000
Share based compensation arrangement by share based payment award options grants in period gross								10,000			50,000
Share based compensation arrangement by share based payment award percentage of fair market Person holding more then 10% voting stock									110.00%			110.00%