Property and Equipment, Net - Property and Equipment, Net (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 92,227	$ 74,120
Accumulated depreciation	(59,929)	(48,430)
Property and equipment, net	32,298	25,690
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	53,349	43,513
Office equipment, including data processing equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	18,550	14,667
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,092	6,836
Furniture, fixtures, and equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,450	3,998
Projects in progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 6,786	$ 5,106