Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended
	Aug. 31, 2019	Nov. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Carrying Amount	$ 1,185,800	$ 746,400
Investment in associated company	2,346,297	2,417,332	$ 2,450,901	$ 2,066,829
Automobile Loan
Variable Interest Entity [Line Items]
Loans receivables securitized	227,400
Other investment vehicles
Variable Interest Entity [Line Items]
Carrying Amount	504,900	203,600
Unfunded equity commitment related to investments	18,000	11,100
Agency Mortgage-Backed Securitizations
Variable Interest Entity [Line Items]
Carrying Amount	1,712,900	2,913,000
Nonagency Mortgage- And Asset-Backed Securitizations
Variable Interest Entity [Line Items]
Carrying Amount	191,200	170,500
JCP Entities | Private Equity Vehicles
Variable Interest Entity [Line Items]
Equity commitments	139,300	139,300
Funded equity commitments	121,700	121,300
Carrying amount of equity investment	28,700	$ 35,500
FXCM
Variable Interest Entity [Line Items]
Fair value of senior secured term loan receivable	58,600
Investment in associated company	72,800
Senior secured term loan receivable and investments in associated companies	$ 131,400