Investment in Securities - Allowance for Credit Losses for Available-for-Sale Securities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Current period adjustments	$ (12,865)
Corporate debt securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Current period adjustments	(12,499)
Residential mortgage-backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Current period adjustments	(236)
Collateralized debt securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Current period adjustments	$ (130)