Capital Requirements (Details) - USD ($)	Apr. 02, 2021	Mar. 31, 2021	Jan. 02, 2021	Dec. 31, 2020
MSCO [Member]
Net capital		$ 29,200,000		$ 27,500,000
Minimum net capital required		2,400,000		2,300,000
Net capital in excess of minimum requirement		$ 26,800,000		$ 25,200,000
Percentage of aggregate debit balance to net capital		24.70%		24.30%
Cash deposits		$ 333,000,000.0		$ 324,900,000
Minimum cash deposits required		323,700,000		319,900,000
Cash deposits in excess of minimum requirement		9,300,000		5,000,000.0
MSCO [Member] | Subsequent Event [Member]
Cash deposits in excess of minimum requirement	$ 9,300,000
StockCross [Member]
Cash deposits in excess of minimum requirement			$ 1,000,000.0
WPS [Member]
Net capital		3,300,000		3,900,000
Minimum net capital required		250,000		250,000
Net capital in excess of minimum requirement		$ 3,100,000		$ 3,700,000