Regulatory Authorities - Additional Information (Detail)	Dec. 31, 2016 USD ($)
LFNY [Member]
Regulatory Requirements [Line Items]
Specified fixed percentage, minimum required capital	6.67%
Minimum net capital requirement as defined under securities exchange act	$ 100,000
Regulatory capital	182,571,000
Regulatory capital in excess of minimum requirement	$ 176,352,000
Aggregate indebtedness to net capital ratio	0.51
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	$ 125,426,000
Regulatory capital in excess of minimum requirement	109,581,000
CFLF [Member]
Regulatory Requirements [Line Items]
Regulatory capital	131,227,000
Regulatory capital in excess of minimum requirement	94,318,000
Combined European Regulated Group [Member]
Regulatory Requirements [Line Items]
Regulatory capital	159,102,000
Regulatory capital in excess of minimum requirement	84,949,000
Other U.S. and Non-U.S. Subsidiaries [Member]
Regulatory Requirements [Line Items]
Regulatory capital	123,351,000
Regulatory capital in excess of minimum requirement	$ 98,902,000