Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2020	Nov. 30, 2019	Jun. 30, 2019	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2020	Aug. 31, 2019	Dec. 01, 2019
Loans and Leases Receivable Disclosure [Line Items]
Receivables from brokers, dealers and clearing organizations	$ 2,755,800	$ 3,011,000		$ 2,755,800		$ 2,755,800
Receivables from customers of securities operations	956,800	1,490,900		956,800		956,800
Other investments with fair values not readily determinable	104,800	172,800		104,800		104,800
Impairment losses on investments				300	$ 2,300	20,900	$ 2,300
Capitalized interest				1,600		6,400
Payables to brokers, dealers and clearing organizations	2,546,500	2,621,700		2,546,500		2,546,500
Payables to customers of securities operations	3,936,800	3,808,600		3,936,800		3,936,800
Cash paid during the year for:
Interest						880,853	1,257,311
Income tax payments (refunds), net						(13,514)	25,825
Operating lease, ROU assets								$ 545,800
Lease liabilities	598,116			598,116		$ 598,116		$ 614,900
Accounting Standards Update [Extensible List]						us-gaap:AccountingStandardsUpdate201602Member
Iowa Premium
Cash paid during the year for:
Membership interest purchase agreement, aggregate ownership interests to purchase			100.00%
National Beef
Cash paid during the year for:
Membership interest purchase agreement, proportionate share			$ 49,000
HomeFed
Cash paid during the year for:
Non-cash investing activities, issuance of common stock related to acquisition							$ 178,800
Foursight Capital | Automobile Loan
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	$ 734,500	$ 741,200		734,500		$ 734,500
Foursight Capital | Automobile Loan | Credit concentration risk | Loans receivable | Prime
Loans and Leases Receivable Disclosure [Line Items]
Concentration risk, percentage	14.00%	15.00%
Foursight Capital | Automobile Loan | Credit concentration risk | Loans receivable | Near-Prime
Loans and Leases Receivable Disclosure [Line Items]
Concentration risk, percentage	52.00%	53.00%
Foursight Capital | Automobile Loan | Credit concentration risk | Loans receivable | Subprime
Loans and Leases Receivable Disclosure [Line Items]
Concentration risk, percentage	34.00%	32.00%
Foursight Capital | Securitized Vehicles
Loans and Leases Receivable Disclosure [Line Items]
Loans receivable	$ 600,500	$ 621,200		$ 600,500		$ 600,500