Property and Equipment, net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Property and Equipment, net
Property and equipment, gross	$ 95,320		$ 95,320		$ 50,655
Less: Accumulated depreciation	(27,342)		(27,342)		(19,924)
Total property and equipment, net	67,978		67,978		30,731
Property and equipment capitalized but not placed in service	37,400		37,400		8,100
Total depreciation and amortization expense	4,477	$ 3,388	12,521	$ 9,474
Property and Equipment
Property and Equipment, net
Total depreciation and amortization expense	3,400	2,400	9,400	6,200
Computer equipment, software, and internally developed software
Property and Equipment, net
Property and equipment, gross	50,718		50,718		37,110
Furniture and fixtures
Property and Equipment, net
Property and equipment, gross	3,124		3,124		2,335
Leasehold Improvements
Property and Equipment, net
Property and equipment, gross	5,245		5,245		4,611
Capitalized facility leases
Property and Equipment, net
Property and equipment, gross	36,233		36,233		6,599
Interest costs related to premises	500		1,600
Lease financing obligation	28,900		28,900		6,600
Internally developed software
Property and Equipment, net
Amortization	2,400	$ 1,700	6,400	$ 3,900
Santa Monica capitalized facility lease
Property and Equipment, net
Property and equipment capitalized but not placed in service	$ 27,600		$ 27,600
San Francisco capitalized facility lease
Property and Equipment, net
Property and equipment capitalized but not placed in service					$ 6,600