Investments - Unrealized Gains or (Losses) Included in Other Comprehensive Income (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gains/Losses included in Other Comprehensive Income for Assets Held at the End of the Period	$ 6,469	$ 30,367
Asset- backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gains/Losses included in Other Comprehensive Income for Assets Held at the End of the Period	(250)	441
Collateralized debt obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gains/Losses included in Other Comprehensive Income for Assets Held at the End of the Period	(5,046)	6,306
Corporates
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gains/Losses included in Other Comprehensive Income for Assets Held at the End of the Period	$ 11,765	$ 23,620