Investments - Unrealized Gains or (Losses) Included in Other Comprehensive Income (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 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	$ 5,786	$ 41,759
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	(318)	1,043
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	(5,220)	5,745
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	$ 11,324	$ 34,971