Regulatory Authorities - Additional Information (Detail)	Dec. 31, 2019 USD ($)
LFNY [Member]
Regulatory Requirements [Line Items]
Specified fixed percentage, minimum required capital	6.67%
Minimum net capital requirement as defined under exchange act	$ 5,000
Regulatory capital	134,374,000
Regulatory capital in excess of minimum requirement	$ 127,427,000
Aggregate indebtedness to net capital ratio	0.78
LFNY [Member] | Maximum [Member]
Regulatory Requirements [Line Items]
Aggregate indebtedness to net capital ratio	15
U.K. Subsidiaries [Member]
Regulatory Requirements [Line Items]
Regulatory capital	$ 175,890,000
Regulatory capital in excess of minimum requirement	158,700,000
CFLF [Member]
Regulatory Requirements [Line Items]
Regulatory capital	127,935,000
Regulatory capital in excess of minimum requirement	69,150,000
Combined European Regulated Group [Member]
Regulatory Requirements [Line Items]
Regulatory capital	182,054,000
Regulatory capital in excess of minimum requirement	75,566,000
Other U.S. and Non-U.S. Subsidiaries [Member]
Regulatory Requirements [Line Items]
Regulatory capital	153,707,000
Regulatory capital in excess of minimum requirement	$ 124,392,000