Capital Requirements (Details) - USD ($)	Oct. 02, 2021	Sep. 30, 2021	Jan. 02, 2021	Dec. 31, 2020
MSCO [Member]
Net capital		$ 35,500,000		$ 27,500,000
Minimum net capital required		2,100,000		2,300,000
Net capital in excess of minimum requirement		$ 33,400,000		$ 25,200,000
Percentage of aggregate debit balance to net capital		33.80%		24.30%
Cash deposits		$ 327,400,000		$ 324,900,000
Minimum cash deposits required		297,400,000		319,900,000
Cash deposits in excess of minimum requirement	$ 27,500,000	30,000,000	$ 1,000,000.0	5,000,000.0
WPS [Member]
Net capital		3,200,000		3,900,000
Minimum net capital required		250,000		250,000
Net capital in excess of minimum requirement		$ 3,000,000.0		$ 3,700,000