Credit Losses - Investments Held at Amortized Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Interest Income	$ 138	$ 84
U.S. Treasury bills
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Interest Income	65	58
Held-to-maturity, allowance for credit loss	0
Corporate bonds
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Interest Income	15	9
Collateralized mortgage obligations
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Interest Income	53	12
Held-to-maturity, allowance for credit loss	0
Yankees
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Interest Income	5	$ 5
Level 2
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized Costs	19,279		$ 18,558
Level 2 | U.S. Treasury bills
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized Costs	10,785		10,784
Level 2 | Corporate bonds
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized Costs	1,705		1,705
Level 2 | Collateralized mortgage obligations
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized Costs	6,192		5,472
Level 2 | Yankees
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Amortized Costs	$ 597		$ 597