Property and Equipment - Components (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property and equipment, net
Property and equipment, gross	$ 125,612	$ 119,011
Accumulated amortization on office equipment held under capital leases	(7,826)	(6,244)
Accumulated depreciation	(57,356)	(53,157)
Property and equipment, net	60,430	59,610
Furniture, fixtures, and leasehold improvements
Property and equipment, net
Property and equipment, gross	9,016	6,249
Office equipment
Property and equipment, net
Property and equipment, gross	18,092	15,214
Office equipment held under capital lease
Property and equipment, net
Property and equipment, gross	19,715	18,531
Computer equipment and software
Property and equipment, net
Property and equipment, gross	62,734	57,389
Construction in progress
Property and equipment, net
Property and equipment, gross	$ 16,055	$ 21,628