Investment Securities - Allowance for Credit Loss Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, allowance for credit loss	$ 855	$ 855
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, allowance for credit loss	855	855	$ 897	$ 0	$ 0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Not to Sell before Recovery, Credit Loss, Previously Recorded, Expense (Reversal)	$ 42	$ (555)
Corporate Bonds [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, allowance for credit loss				$ 300