Leases - Narrative (Details)		12 Months Ended
	Sep. 30, 2018 USD ($)	Jan. 31, 2020 USD ($) ft²	Jan. 31, 2019 USD ($)	Jan. 31, 2018 USD ($)	Feb. 29, 2020 USD ($)	Dec. 31, 2019 ft²	Oct. 31, 2019 USD ($) ft²	Oct. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	Aug. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)
Lessee, Lease, Description [Line Items]
Rentable office space (in sqft) | ft²		106,230
Term of contract		12 years
Total minimum payments		$ 83,566,000
Option to extend		P5Y
Rent expense	$ 1,500,000		$ 10,700,000	$ 9,100,000
Operating lease, liability		$ 11,863,000
Term of lease						12 years	5 years
NY Office Lease
Lessee, Lease, Description [Line Items]
Total minimum payments		87,300,000
Operating lease, liability		0
Area of leased space (in sq ft) | ft²							21,000
Lease not yet commenced, estimated base rent payments							$ 8,100,000
Operating Lease in New York
Lessee, Lease, Description [Line Items]
Letters of credit outstanding										$ 500,000	$ 1,100,000
Operating Lease in Texas
Lessee, Lease, Description [Line Items]
Letters of credit outstanding							$ 300,000		$ 400,000
Operating Lease in Australia
Lessee, Lease, Description [Line Items]
Letters of credit outstanding								$ 200,000
Dublin Lease
Lessee, Lease, Description [Line Items]
Area of leased space (in sq ft) | ft²						40,000
Lease not yet commenced, estimated base rent payments		$ 27,000,000.0
Subsequent Event | Operating Lease in Australia
Lessee, Lease, Description [Line Items]
Letters of credit outstanding					$ 500,000