Investments Additional Information (Details)		3 Months Ended				9 Months Ended
	Jan. 02, 2018 USD ($) $ / shares	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) day security shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2019 USD ($) day security shares	Sep. 30, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($) security	Jul. 24, 2018 $ / shares	Oct. 25, 2017 $ / shares
Debt Securities, Available-for-sale [Line Items]
Securities in unrealized loss positions | security				33		33		64
Other-than-temporary impairment loss				$ 0	$ 0	$ 75,000	$ 0
Limited liability investments				3,838,000		3,838,000		$ 4,790,000
(Gain) loss on change in fair value of limited liability investments, at fair value				(3,356,000)	(131,000)	3,256,000	(1,592,000)
Limited liability investments, at fair value				29,559,000		29,559,000		26,015,000
Investment impairment losses				0	100,000	0	100,000
Unfunded commitments				600,000		600,000
Investments in private companies, at adjusted cost				2,035,000		2,035,000		3,090,000
Net change in unrealized (loss) gain on private company investments				(343,000)	$ 19,000	(324,000)	(136,000)
Other-than-temporary impairment loss						75,000	$ 0
Real estate investments				10,662,000		10,662,000		10,662,000
Other investments				$ 750,000		$ 750,000		2,079,000
Stock price threshold trading days | day				20		20
Threshold trading days | day				30		30
Restricted cash				$ 20,762,000		$ 20,762,000		16,959,000
Variable Interest Entity, Primary Beneficiary
Debt Securities, Available-for-sale [Line Items]
Unfunded commitments				$ 600,000		$ 600,000
Performance Share Grant Agreement
Debt Securities, Available-for-sale [Line Items]
Stock reserved for future issuances (in shares) | shares				475,000		475,000
Minimum
Debt Securities, Available-for-sale [Line Items]
Stock reserved for future issuances (in shares) | shares				100,000		100,000
Share price (in dollars per share) | $ / shares	$ 10				$ 10.00		$ 10.00
Maximum
Debt Securities, Available-for-sale [Line Items]
Share price (in dollars per share) | $ / shares					18		18		$ 18.00
Clause 2
Debt Securities, Available-for-sale [Line Items]
Stock reserved for future issuances (in shares) | shares				125,000		125,000
Share price (in dollars per share) | $ / shares					12.00		12.00		12.00
Clause 1 and 2
Debt Securities, Available-for-sale [Line Items]
Stock reserved for future issuances (in shares) | shares				225,000		225,000
Clause 3
Debt Securities, Available-for-sale [Line Items]
Share price (in dollars per share) | $ / shares					$ 15		$ 15		$ 15.00
Clause 1, 2 and 3
Debt Securities, Available-for-sale [Line Items]
Stock reserved for future issuances (in shares) | shares				350,000		350,000
Management
Debt Securities, Available-for-sale [Line Items]
Share price (in dollars per share) | $ / shares										$ 7.85
Proceeds from termination of contract	$ 300,000
Proceeds from sale of available-for-sale debt securities					$ 1,000,000		$ 1,300,000
Mendota
Debt Securities, Available-for-sale [Line Items]
Escrow deposit				$ 5,100,000		$ 5,100,000		5,000,000
IWS
Debt Securities, Available-for-sale [Line Items]
Restricted cash				13,500,000		13,500,000		10,000,000
State and Provincial Regulatory Authorities
Debt Securities, Available-for-sale [Line Items]
Restricted cash equivalents				200,000		200,000		200,000
Restricted cash				1,900,000		1,900,000		1,900,000
Third Parties
Debt Securities, Available-for-sale [Line Items]
Restricted cash				300,000		300,000		100,000
Private Company Investments
Debt Securities, Available-for-sale [Line Items]
Other-than-temporary impairment loss					0
Net change in unrealized (loss) gain on private company investments					0		(100,000)
Other-than-temporary impairment loss				200,000	$ 0	200,000	$ 0
Significant Other Observable Inputs (Level 2)
Debt Securities, Available-for-sale [Line Items]
Real estate investments				0		0		0
Other investments				750,000		$ 750,000		$ 2,079,000
1347 Investors LLC
Debt Securities, Available-for-sale [Line Items]
Ownership interest						26.70%
Subsequent Event
Debt Securities, Available-for-sale [Line Items]
Investment impairment losses		$ 700,000
Other than temporary impairment losses, investments, percent		90.00%
1347 Investors LLC
Debt Securities, Available-for-sale [Line Items]
(Gain) loss on change in fair value of limited liability investments, at fair value				$ (2,700,000)
1347 Investors LLC | Subsequent Event
Debt Securities, Available-for-sale [Line Items]
(Gain) loss on change in fair value of limited liability investments, at fair value		$ (600,000)	$ (700,000)