SCHEDULE I - Summary of Investments - Other than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2019 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown on Balance Sheet	$ 1,948,891
Bank loan participations, held-for-investment, net of allowance
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	260,864
Fair Value	252,423
Amount at which shown on Balance Sheet	260,864
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	156,925
Fair Value	156,925
Amount at which shown on Balance Sheet	156,925
Other invested assets
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown on Balance Sheet	16,741
Available-for-sale Securities | Fixed maturity securities:
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	1,398,533
Fair Value	1,433,626
Amount at which shown on Balance Sheet	1,433,626
Available-for-sale Securities | State and municipal
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	159,894
Fair Value	167,101
Amount at which shown on Balance Sheet	167,101
Available-for-sale Securities | Residential mortgage-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	261,524
Fair Value	264,146
Amount at which shown on Balance Sheet	264,146
Available-for-sale Securities | Corporate
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	611,304
Fair Value	632,221
Amount at which shown on Balance Sheet	632,221
Available-for-sale Securities | Commercial mortgage and asset-backed
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	249,309
Fair Value	252,457
Amount at which shown on Balance Sheet	252,457
Available-for-sale Securities | U.S. Treasury securities and obligations guaranteed by the U.S. government
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	114,477
Fair Value	115,667
Amount at which shown on Balance Sheet	115,667
Available-for-sale Securities | Redeemable preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	2,025
Fair Value	2,034
Amount at which shown on Balance Sheet	2,034
Available-for-sale Securities | Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	73,244
Fair Value	80,735
Amount at which shown on Balance Sheet	80,735
Available-for-sale Securities | Preferred stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	52,557
Fair Value	62,747
Amount at which shown on Balance Sheet	62,747
Available-for-sale Securities | Common stock
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost or Amortized Cost	20,687
Fair Value	17,988
Amount at which shown on Balance Sheet	$ 17,988