Regulatory Authorities - Additional Information (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
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	79,663,000
Regulatory capital in excess of minimum requirement	$ 74,877,000
Aggregate indebtedness to net capital ratio	0.90
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	$ 128,206,000
Regulatory capital in excess of minimum requirement	112,123,000
CFLF [Member]
Regulatory Requirements [Line Items]
Regulatory capital	133,162,000
Regulatory capital in excess of minimum requirement	88,708,000
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	120,725,000
Regulatory capital in excess of minimum requirement	$ 94,924,000