Long-Term Investments (Combined Financial Statements for Unconsolidated Subsidiaries Accounted for on Equity Method) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Indian Creek and Boyar Value Fund
Schedule of Equity Method Investments [Line Items]
Investment securities	$ 210,685		$ 33,830
Cash and cash equivalents	26,088		521
Other assets	1,861		33
Total assets	238,634		34,384
Other liabilities	85,623		738
Total liabilities	85,623		738
Partners’ capital	153,011		33,646
Total liabilities and partners’ capital	238,634		34,384
Revenues	2,834		549		$ 792
Expenses	6,756		861		690
Gross profit	(3,922)		(312)		102
Total net realized gain (loss) and net change in unrealized depreciation from investments	18,822		(5,781)		100
Income from continuing operations	$ 14,900		$ (6,093)		$ 202
Ladenburg Thalmann Financial Services
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents		$ 251,033		$ 262,834
Receivables from clearing brokers, note receivable and other receivable, net		175,600		165,149
Goodwill and intangible assets, net		188,975		200,199
Other assets		202,516		172,409
Total assets		818,124		800,591
Other liabilities		73,380		37,658
Accrued compensation, commissions and fees payable		142,875		141,260
Accounts payable and accrued liabilities		37,197		50,122
Notes payable, net of $5,881 and $115 unamortized discount in 2019 and 2018, respectively		315,898		185,199
Unamortized discount		5,881		115
Total liabilities		569,350		414,239
Preferred stock		2		2
Common stock		15		20
Additional paid-in capital		317,735		487,752
Accumulated deficit		(68,971)		(101,467)
Total controlling shareholders’ equity		248,781		386,307
Non-controlling interest		(7)		45
Partners’ capital		248,774		386,352
Total liabilities and partners’ capital		818,124		800,591
Revenues		1,428,688		1,380,031		$ 1,221,195
Expenses		1,385,699		1,345,768		1,217,331
Gross profit		42,989		34,263		3,864
Change in fair value of contingent consideration		(363)		(232)		48
Income from continuing operations		42,626		34,031		3,912
Net income		$ 31,779		$ 30,858		$ 1,669