Property and Equipment - Components (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Property and equipment, net
Property and equipment, gross	$ 146,957	$ 139,395
Accumulated amortization on office equipment held under capital leases	(12,499)	(10,143)
Accumulated depreciation	(76,325)	(68,990)
Property and equipment, net	58,133	60,262
Furniture, fixtures, and leasehold improvements
Property and equipment, net
Property and equipment, gross	9,030	9,431
Office equipment
Property and equipment, net
Property and equipment, gross	18,444	19,619
Office equipment held under capital lease
Property and equipment, net
Property and equipment, gross	20,952	20,916
Computer equipment and software
Property and equipment, net
Property and equipment, gross	85,627	74,844
Construction in progress
Property and equipment, net
Property and equipment, gross	$ 12,904	$ 14,585