Regulatory Authorities - Additional Information (Detail) - USD ($)	Jun. 30, 2018	Mar. 31, 2018
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	109,681,000
Regulatory capital in excess of minimum requirement	$ 106,644,000
Aggregate indebtedness to net capital ratio	0.42
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	$ 166,717,000
Regulatory capital in excess of minimum requirement	148,324,000
CFLF [Member]
Regulatory Requirements [Line Items]
Regulatory capital	130,702,000
Regulatory capital in excess of minimum requirement	76,071,000
Combined European Regulated Group [Member]
Regulatory Requirements [Line Items]
Regulatory capital		$ 176,098,000
Regulatory capital in excess of minimum requirement		$ 63,607,000
Other U.S. and Non-U.S. Subsidiaries [Member]
Regulatory Requirements [Line Items]
Regulatory capital	158,343,000
Regulatory capital in excess of minimum requirement	$ 130,629,000