Capital Requirements (Details) - USD ($)	Jul. 02, 2021	Jun. 30, 2021	Jan. 02, 2021	Dec. 31, 2020
MSCO [Member]
Net capital		$ 31,600,000		$ 27,500,000
Minimum net capital required		2,100,000		2,300,000
Net capital in excess of minimum requirement		$ 29,500,000		$ 25,200,000
Percentage of aggregate debit balance to net capital		30.60%		24.30%
Cash deposits		$ 348,700,000		$ 324,900,000
Minimum cash deposits required		332,700,000		319,900,000
Cash deposits in excess of minimum requirement		16,000,000		5,000,000.0
MSCO [Member] | Subsequent Event [Member]
Cash deposits in excess of minimum requirement	$ 1,500,000
StockCross [Member]
Cash deposits in excess of minimum requirement			$ 1,000,000.0
WPS [Member]
Net capital		2,800,000		3,900,000
Minimum net capital required		250,000		250,000
Net capital in excess of minimum requirement		$ 2,500,000		$ 3,700,000