Geographic Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 54,856	$ 48,270	$ 44,346	$ 37,657	$ 36,426	$ 30,768	$ 26,718	$ 24,002	$ 185,129	$ 117,914	$ 73,022
Reduction of revenue relating to common stock warrants									0	0	2,500
Property and equipment, net	14,436				7,947				14,436	7,947
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									128,983	81,837	50,874
Reduction of revenue relating to common stock warrants											2,500
Property and equipment, net	10,455				7,529				10,455	7,529
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									19,448	12,930	8,612
Property and equipment, net	3,185				343				3,185	343
All Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									36,698	23,147	13,536
Property and equipment, net	$ 796				$ 75				$ 796	$ 75