Regulatory Authorities - Additional Information (Detail)	Dec. 31, 2018 USD ($)
LFNY [Member]
Regulatory Requirements [Line Items]
Specified fixed percentage, minimum required capital	6.67%
Minimum net capital requirement as defined under exchange act	$ 100,000
Regulatory capital	174,732,000
Regulatory capital in excess of minimum requirement	$ 171,679,000
Aggregate indebtedness to net capital ratio	0.26
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	$ 162,350,000
Regulatory capital in excess of minimum requirement	142,542,000
CFLF [Member]
Regulatory Requirements [Line Items]
Regulatory capital	136,110,000
Regulatory capital in excess of minimum requirement	81,336,000
Combined European Regulated Group [Member]
Regulatory Requirements [Line Items]
Regulatory capital	157,783,000
Regulatory capital in excess of minimum requirement	56,330,000
Other U.S. and Non-U.S. Subsidiaries [Member]
Regulatory Requirements [Line Items]
Regulatory capital	149,252,000
Regulatory capital in excess of minimum requirement	$ 121,863,000