Schedule I Summary Of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	$ 6,475,530
Allowance for Credit Losses	(948)
Fair Value	6,845,941
Amount Reflected on the Consolidated Balance Sheet	6,845,941
Reinvested Cash Collateral Held Under Securities Lending Agreements	15,587	$ 25,561
Loaned securities	57,499	$ 66,442
US government and agency securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	176,033
Allowance for Credit Losses	0
Fair Value	174,099
Amount Reflected on the Consolidated Balance Sheet	174,099
State and municipal obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	149,258
Allowance for Credit Losses	0
Fair Value	165,271
Amount Reflected on the Consolidated Balance Sheet	165,271
Corporate bonds and notes
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	2,832,350
Allowance for Credit Losses	(948)
Fair Value	3,078,415
Amount Reflected on the Consolidated Balance Sheet	3,078,415
RMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	799,814
Allowance for Credit Losses	0
Fair Value	833,939
Amount Reflected on the Consolidated Balance Sheet	833,939
CMBS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	645,071
Allowance for Credit Losses	0
Fair Value	681,265
Amount Reflected on the Consolidated Balance Sheet	681,265
CLO
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	569,173
Allowance for Credit Losses	0
Fair Value	568,558
Amount Reflected on the Consolidated Balance Sheet	568,558
Other ABS
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	249,988
Allowance for Credit Losses	0
Fair Value	252,457
Amount Reflected on the Consolidated Balance Sheet	252,457
Foreign government and agency securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	5,100
Allowance for Credit Losses	0
Fair Value	5,438
Amount Reflected on the Consolidated Balance Sheet	5,438
Total fixed-maturities available for sale
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	5,426,787
Allowance for Credit Losses	(948)
Fair Value	5,759,442
Amount Reflected on the Consolidated Balance Sheet	5,759,442
Total fixed-maturities available for sale | Securities Financing Transaction, Fair Value
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Loaned securities	36,100
Trading securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	260,863
Allowance for Credit Losses	0
Fair Value	290,983
Amount Reflected on the Consolidated Balance Sheet	290,983
Reinvested Cash Collateral Held Under Securities Lending Agreements	15,600
Common stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	166,721
Allowance for Credit Losses	0
Fair Value	172,539
Amount Reflected on the Consolidated Balance Sheet	172,539
Total equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	166,721
Allowance for Credit Losses	0
Fair Value	172,539
Amount Reflected on the Consolidated Balance Sheet	172,539
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	618,014
Allowance for Credit Losses	0
Fair Value	618,004
Amount Reflected on the Consolidated Balance Sheet	618,004
Short-term investments | Securities Financing Transaction, Fair Value
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Loaned securities	100
Other invested assets
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amortized Cost	3,145
Allowance for Credit Losses	0
Fair Value	4,973
Amount Reflected on the Consolidated Balance Sheet	4,973
Equity securities | Securities Financing Transaction, Fair Value
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Loaned securities	$ 21,300