Commitments and Contingencies - San Francisco Lease Termination (Details) - USD ($) $ in Thousands	1 Months Ended
	Jul. 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Operating Leased Assets [Line Items]
Accrued expenses and other liabilities			$ 17,561	$ 12,897	$ 12,790
Capitalized facility lease asset			147,389		135,991
Capitalized facility leases
Operating Leased Assets [Line Items]
Capitalized facility lease asset			$ 38,351		$ 39,302
Office lease | San Francisco office
Operating Leased Assets [Line Items]
Decrease in future commitment	$ 4,500
Lease remaining term	6 years
Forecast | San Francisco office
Operating Leased Assets [Line Items]
Accrued expenses and other liabilities		$ 6,900
Forecast | San Francisco office | Capitalized facility leases
Operating Leased Assets [Line Items]
Capitalized facility lease asset		$ 6,900