Segment Information - Reconciliation of Revenue from Segments to Consolidated (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues from contracts with customers	$ 112.9	$ 74.8	$ 305.9	$ 224.3
Other Revenue	(123.0)	384.7	288.9	435.6
Total revenues	(10.1)	459.5	594.8	659.9
HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Other Revenue	7.4	14.5	18.1	58.1
Total revenues	7.4	14.5	18.1	58.1
Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Other Revenue	217.7		457.3
Total revenues	217.7	0.0	457.3	0.0
NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	82.3	70.7	241.4	211.8
Other Revenue	0.0	0.0	0.0	0.0
Total revenues	82.3	70.7	241.4	211.8
Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Other Revenue	28.5	16.3	88.8	21.0
Total revenues	28.5	16.3	88.8	21.0
Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	30.6	4.1	64.5	12.5
Other Revenue	(376.6)	353.9	(275.3)	356.5
Total revenues	(346.0)	358.0	(210.8)	369.0
United Kingdom
Segment Reporting Information [Line Items]
Revenues from contracts with customers	13.0	13.9	39.9	36.3
United Kingdom | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
United Kingdom | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
United Kingdom | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	13.0	13.9	39.9	36.3
United Kingdom | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
United Kingdom | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Specialty Transportation (1)
Segment Reporting Information [Line Items]
Revenues from contracts with customers	25.7	21.9	73.0	66.1
Specialty Transportation (1) | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Specialty Transportation (1) | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Specialty Transportation (1) | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	25.7	21.9	73.0	66.1
Specialty Transportation (1) | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Specialty Transportation (1) | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Real Estate
Segment Reporting Information [Line Items]
Revenues from contracts with customers	6.2	6.0	25.2	32.7
Real Estate | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Real Estate | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Real Estate | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	6.2	6.0	25.2	32.7
Real Estate | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Real Estate | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Social Services
Segment Reporting Information [Line Items]
Revenues from contracts with customers	10.2	8.6	26.2	22.2
Social Services | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Social Services | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Social Services | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	10.2	8.6	26.2	22.2
Social Services | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Social Services | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Pet
Segment Reporting Information [Line Items]
Revenues from contracts with customers	19.9	14.7	55.6	39.8
Pet | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Pet | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Pet | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	19.9	14.7	55.6	39.8
Pet | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Pet | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Other
Segment Reporting Information [Line Items]
Revenues from contracts with customers	9.7	7.7	28.5	20.8
Other | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Other | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Other | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	7.3	5.6	21.5	14.7
Other | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Other | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	2.4	2.1	7.0	6.1
Total commission and other revenue
Segment Reporting Information [Line Items]
Revenues from contracts with customers	84.7	72.8	248.4	217.9
Total commission and other revenue | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Total commission and other revenue | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Total commission and other revenue | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	82.3	70.7	241.4	211.8
Total commission and other revenue | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Total commission and other revenue | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	2.4	2.1	7.0	6.1
Product and service revenues
Segment Reporting Information [Line Items]
Revenues from contracts with customers	28.2	2.0	57.5	6.4
Product and service revenues | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Product and service revenues | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0		0.0
Product and service revenues | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Product and service revenues | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0	0.0	0.0
Product and service revenues | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	$ 28.2	$ 2.0	$ 57.5	$ 6.4