Property and equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property and equipment
Total property and equipment, gross	$ 4,304,997	$ 2,947,464
Less: Accumulated depreciation and amortization	(2,106,357)	(1,551,310)
Total property and equipment, net	2,198,640	1,396,154
Depreciation and amortization expense	554,765	532,784	656,837
Equipment
Property and equipment
Total property and equipment, gross	939,129	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
Total property and equipment, gross	2,493,658	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
Total property and equipment, gross	182,562	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
Total property and equipment, gross	$ 689,648	$ 263,691
Leasehold improvements | Minimum
Property and equipment
Estimated useful life	5 years
Leasehold improvements | Maximum
Property and equipment
Estimated useful life	9 years