LEASES (Details) $ in Millions	1 Months Ended	3 Months Ended
	Sep. 30, 2019 USD ($) ft²	Mar. 31, 2020 USD ($)	Sep. 30, 2017
Leases
Options to renew		true
Additional right of use assets		$ 64.2
Additional operating lease liabilities		84.7
Additional operating right of use assets		84.7
Lease incentive for leasehold improvements		20.4
Minimum lease payments		$ 175.1
Old Post Office building in Chicago, Illinois
Leases
Area of office space leased | ft²	185,000
Initial term of lease	187 months
Renewal Term	60 months
Minimum lease payments	$ 98.8
Office Space in Chicago Board of Trade Building
Leases
Area of office space leased | ft²	40,000
Initial term of lease	150 months
Renewal Term			60 months
Minimum lease payments	$ 17.1
Minimum
Leases
Renewal term		1 year
Maximum
Leases
Renewal term		5 years
Option to terminate period		1 year