Property and equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and equipment
Property and equipment, gross	$ 2,947,464	$ 2,794,011
Less: Accumulated depreciation and amortization	(1,551,310)	(1,570,449)
Property and equipment, net	1,396,154	1,223,562
Depreciation and amortization expense	532,784	656,837	502,250
Assets disposed off that were either destroyed or were determined to no longer be in service	100,000	1,000,000
Equipment
Property and equipment
Estimated useful life	5 years
Property and equipment, gross	923,356	1,102,132
Computer hardware
Property and equipment
Estimated useful life	5 years
Property and equipment, gross	1,688,262	1,292,504
Furniture and fixtures
Property and equipment
Property and equipment, gross	72,155	77,779
Furniture and fixtures | Minimum
Property and equipment
Estimated useful life	5 years
Furniture and fixtures | Maximum
Property and equipment
Estimated useful life	7 years
Leasehold improvements
Property and equipment
Property and equipment, gross	$ 263,691	$ 321,596
Leasehold improvements | Minimum
Property and equipment
Estimated useful life	5 years
Leasehold improvements | Maximum
Property and equipment
Estimated useful life	7 years