Income Taxes Summary of Operating Loss Carryforwards (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Income Taxes Receivable	$ 1,200,000
Deferred Tax Assets, Gross	76,109,000	$ 144,056,000
Deferred Tax Liabilities, Gross	61,885,000	59,656,000
Income (Loss) from Continuing Operations before Income Taxes, Domestic	289,600,000	68,900,000	$ 93,000,000.0
Deferred Tax Assets, Other	2,858,000	3,043,000
Deferred Tax Assets, Valuation Allowance	5,194,000	5,234,000
Deferred Income Tax Expense (Benefit)	70,118,000	13,296,000	18,965,000
Income (Loss) from Continuing Operations before Income Taxes, Foreign	7,900,000	$ 2,200,000	$ 6,000,000.0
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	6,200,000
Tax Credit Carryforward, Valuation Allowance	4,200,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	60,500,000
Inland Revenue, Hong Kong [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	12,400,000
New York State Division of Taxation and Finance [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	33,600,000
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	26,000,000.0
Luxembourg Reinsurance Companies [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Liabilities, Gross	110,300,000
Deferred Tax Assets, Other	214,100,000
Deferred Tax Assets, Valuation Allowance	214,100,000
LaBranche and Co Inc. [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	23,600,000
Deferred tax asset, deduction limitation	$ 6,700,000