Income taxes (Detail) - Significant components of deferred tax assets and liabilities and related valuation allowances (USD $)	Dec. 31, 2012	Dec. 31, 2011
Non-operating loss carryforward	$ 16,512,538	$ 16,152,227
Share-based compensation	2,235,711	2,226,186
R&D tax credit carryforward	973,000	973,000
Other	349,028	450,821
Total deferred tax assets	20,070,277	19,802,234
Deferred tax liabilities	(528,808)	(528,808)
Valuation allowance	(19,541,469)	(19,273,426)
Deferred tax assets and liabilities, net