Property and equipment (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Property and equipment
Property and equipment, gross	$ 3,570,656		$ 2,947,464
Less: Accumulated depreciation and amortization	(1,668,718)		(1,551,310)
Property and equipment, net	1,901,938		1,396,154
Depreciation and amortization expense	118,761	139,753
Equipment
Property and equipment
Property and equipment, gross	927,012		923,356
Equipment | Minimum
Property and equipment
Estimated useful life	2 years
Equipment | Maximum
Property and equipment
Estimated useful life	5 years
Computer hardware
Property and equipment
Property and equipment, gross	1,863,187		1,688,262
Computer hardware | Minimum
Property and equipment
Estimated useful life	3 years
Computer hardware | Maximum
Property and equipment
Estimated useful life	5 years
Furniture and fixtures
Property and equipment
Property and equipment, gross	163,891		72,155
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	$ 616,566		$ 263,691
Leasehold improvements | Minimum
Property and equipment
Estimated useful life	5 years
Leasehold improvements | Maximum
Property and equipment
Estimated useful life	7 years