Variable Interest Entities - Non-consolidated VIEs - Additional Information (Detail) - USD ($)	Nov. 30, 2017	Nov. 30, 2016
Variable Interest Entity [Line Items]
Maximum exposure	$ 243,600,000
Agency mortgage-backed securities
Variable Interest Entity [Line Items]
Carrying amount	1,829,600,000	$ 1,002,200,000
Non agency mortgage-backed securities
Variable Interest Entity [Line Items]
Carrying amount	253,200,000	439,400,000
Related party private equity vehicles | JCP Entities
Variable Interest Entity [Line Items]
Equity commitments amount	148,100,000	148,100,000
Funded equity commitments	126,300,000	125,100,000
Carrying amount of equity investment	23,700,000	37,600,000
Related party private equity vehicles | Jefferies Energy Partners I LP
Variable Interest Entity [Line Items]
Maximum exposure		3,000,000.0
Other private investment vehicles
Variable Interest Entity [Line Items]
Equity commitments amount	61,800,000	75,800,000
Funded equity commitments	61,000,000	74,300,000
Carrying amount of equity investment	$ 48,000,000	$ 52,300,000