Schedule I-Summary Of Investments-Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2021 USD ($)
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	$ 2,804,007
Fair Value	3,162,968
Amount at which shown in the balance sheet	3,162,968
Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	2,346,267
Fair Value	2,409,887
Amount at which shown in the balance sheet	2,409,887
Debt Securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	2,346,267
Fair Value	2,409,887
Amount at which shown in the balance sheet	2,409,887
U.S. government | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	127,752
Fair Value	134,554
Amount at which shown in the balance sheet	134,554
U.S. Agency | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	30,403
Fair Value	32,760
Amount at which shown in the balance sheet	32,760
Non-U.S. govt. & agency | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	8,297
Fair Value	8,481
Amount at which shown in the balance sheet	8,481
Agency MBS | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	362,861
Fair Value	367,187
Amount at which shown in the balance sheet	367,187
ABS/CMBS/MBS | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	264,273
Fair Value	264,054
Amount at which shown in the balance sheet	264,054
Corporate Debt | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	925,394
Fair Value	957,095
Amount at which shown in the balance sheet	957,095
Municipal | Available for sale securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	627,287
Fair Value	645,756
Amount at which shown in the balance sheet	645,756
Equity Securities
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	324,501
Fair Value	613,776
Amount at which shown in the balance sheet	613,776
Ind Misc & All Other
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	103,261
Fair Value	190,735
Amount at which shown in the balance sheet	190,735
ETFs (Ind/misc)
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	221,240
Fair Value	423,041
Amount at which shown in the balance sheet	423,041
Cash and Short-term Investments
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	88,804
Fair Value	88,804
Amount at which shown in the balance sheet	88,804
Other Invested Assets
SCHEDULE I - SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES
Cost	44,435
Fair Value	50,501
Amount at which shown in the balance sheet	$ 50,501