Investments - Investment Management Agreement (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) item
Securities of any one issuer (excluding the U.S. Government)
Investments
Number of Investment Committee members required to authorize investment | item	2
Minimum | Securities of any one issuer (excluding the U.S. Government)
Investments
Investments, portfolio allocations requiring additional consent	10.00%
Minimum | Cash investment grade cash equivalents or U . S . treasury securities
Investments
Investments, target portfolio allocations percent	25.00%
Maximum | Securities of any one issuer (excluding the U.S. Government)
Investments
Investments, target portfolio allocations percent	15.00%
Investments, portfolio allocations requiring additional consent	15.00%
Maximum | Single issuer of exchange-traded common equities
Investments
Investments, target portfolio allocations percent	5.00%
Maximum | Common Stock
Investments
Investments, target portfolio allocations, amount | $	$ 100.0
Maximum | Common, preferred or other equity investments
Investments
Investments, target portfolio allocations percent	25.00%
Investor | Clients of FCM, including Mr. Berkowitz
Investments
Common stock ownership percentage	44.24%