Fair Value of Assets and Liabilities - Schedule of Changes in Fair Value of the Company's Level 3 Assets and Liabilities (Detail) - USD ($)		3 Months Ended						6 Months Ended
		Jun. 30, 2018		Mar. 31, 2018		Jun. 30, 2017		Jun. 30, 2017
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance				$ 7,450,000
Ending balance						$ 9,510,000		$ 9,510,000
Fair Value, Measurements, Nonrecurring [Member] | Taxi Medallion Loan Trust III [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance		$ 161,155,000		208,279,000		250,976,000		266,816,000
Gains (losses) included in earnings				(38,190,000)		(12,452,000)		(21,147,000)
Purchases, investments, and issuances				7,000		320,000		320,000
Sales, maturities, settlements, and distributions				(8,941,000)		(5,429,000)		(12,574,000)
Ending balance				161,155,000		233,415,000		233,415,000
Amounts related to held assets				(38,190,000)	[1]	(12,426,000)	[2]	(21,095,000)	[2]
Fair Value, Measurements, Nonrecurring [Member] | Commercial Loan And Lease [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance		93,620,000		90,188,000		73,748,000		83,634,000
Gains (losses) included in earnings				(8,000)		(109,000)		(403,000)
Purchases, investments, and issuances				7,252,000		7,720,000		7,816,000
Sales, maturities, settlements, and distributions				(3,812,000)		(3,267,000)		(12,955,000)
Ending balance				93,620,000		78,092,000		78,092,000
Amounts related to held assets				(10,000)	[1]	(118,000)	[2]	(450,000)	[2]
Fair Value, Measurements, Nonrecurring [Member] | Investment [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance		331,169,000		302,147,000		300,886,000		293,360,000
Gains (losses) included in earnings				29,143,000		930,000		9,054,000
Purchases, investments, and issuances				462,000		402,000		402,000
Sales, maturities, settlements, and distributions				(583,000)		(399,000)		(997,000)
Ending balance				331,169,000		301,819,000		301,819,000
Amounts related to held assets				29,143,000	[1]	930,000	[2]	9,054,000	[2]
Fair Value, Measurements, Nonrecurring [Member] | Equity Investment [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance		9,458,000		9,521,000		9,640,000		8,407,000
Gains (losses) included in earnings		(374,000)		(993,000)		2,894,000		4,155,000
Purchases, investments, and issuances		529,000		935,000		856,000		856,000
Sales, maturities, settlements, and distributions		(217,000)		(5,000)		(3,074,000)		(3,102,000)
Transfers in	[3]	1,377,000
Ending balance		10,773,000		9,458,000		10,316,000		10,316,000
Amounts related to held assets		(374,000)	[4]	(993,000)	[1]	120,000	[2]	1,381,000	[2]
Fair Value, Measurements, Nonrecurring [Member] | Other than Securities Investment [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance		5,535,000		7,450,000		9,510,000		9,510,000
Gains (losses) included in earnings				(1,915,000)
Ending balance				5,535,000		9,510,000		9,510,000
Amounts related to held assets	[1]			(1,915,000)
Fair Value, Measurements, Nonrecurring [Member] | Other Asset [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Beginning balance		$ 339,000		339,000		354,000		354,000
Ending balance				$ 339,000		$ 354,000		$ 354,000

[1] Total realized and unrealized gains (losses) included in income for the period which relate to assets held as of March 31, 2018

[2] Total realized and unrealized gains (losses) included in income for the period which relate to assets held as of June 30, 2017.

[3] Represents the removal of RPAC Racing investments eliminated in consolidation as well as the transfer of LAX from controlled subsidiaries during the 2018 second quarter.

[4] Total realized and unrealized gains (losses) included in income for the period which relate to assets held as of June 30, 2018.