Property and equipment (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Property and equipment
Property and equipment, gross	$ 4,005,846		$ 4,005,846		$ 2,947,464
Less: Accumulated depreciation and amortization	(1,819,570)		(1,819,570)		(1,551,310)
Property and equipment, net	2,186,276		2,186,276		1,396,154
Depreciation and amortization expense	152,730	131,850	271,491	271,603
Equipment
Property and equipment
Property and equipment, gross	929,582		929,582		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	2,246,963		2,246,963		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	179,015		179,015		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	$ 650,286		$ 650,286		$ 263,691
Leasehold improvements | Minimum
Property and equipment
Estimated useful life			5 years
Leasehold improvements | Maximum
Property and equipment
Estimated useful life			9 years