SCHEDULE I - SUMMARY OF INVESTMENTS OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		$ 783,047	$ 600,504
Investments classified as cash and cash equivalents		59,780
Total Investments [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		860,135
Fair value		885,418
Amount at which shown in the balance sheet	[1]	885,132
Fixed Income Securities [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		783,047
Fair value		795,538
Amount at which shown in the balance sheet	[1]	795,538
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		64,306
Fair value		76,812
Amount at which shown in the balance sheet	[1]	76,812
Bonds [Member] | Agency Collateralized Mortgage Obligations [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		11,557
Fair value		12,093
Amount at which shown in the balance sheet	[1]	12,093
Bonds [Member] | Agency Mortgage-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		54,286
Fair value		56,280
Amount at which shown in the balance sheet	[1]	56,280
Bonds [Member] | Asset-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		107,028
Fair value		106,397
Amount at which shown in the balance sheet	[1]	106,397
Bonds [Member] | Bank Loans [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		14,932
Fair value		14,568
Amount at which shown in the balance sheet	[1]	14,568
Bonds [Member] | Certificates of Deposit [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		2,835
Fair value		2,835
Amount at which shown in the balance sheet	[1]	2,835
Bonds [Member] | Collateralized Mortgage Obligations [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		5,123
Fair value		5,616
Amount at which shown in the balance sheet	[1]	5,616
Bonds [Member] | Corporate Securities [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		274,340
Fair value		281,381
Amount at which shown in the balance sheet	[1]	281,381
Bonds [Member] | Mortgage-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		46,685
Fair value		47,463
Amount at which shown in the balance sheet	[1]	47,463
Bonds [Member] | Municipal Obligations [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		35,749
Fair value		36,286
Amount at which shown in the balance sheet	[1]	36,286
Bonds [Member] | Non-U.S. Government Obligations [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		23,889
Fair value		24,179
Amount at which shown in the balance sheet	[1]	24,179
Bonds [Member] | U.S. Government Obligations [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		206,623
Fair value		208,440
Amount at which shown in the balance sheet	[1]	208,440
Common Stocks [Member] | Consumer [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		13,473
Fair value		16,707
Amount at which shown in the balance sheet	[1]	16,707
Common Stocks [Member] | Energy [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		3,618
Fair value		3,074
Amount at which shown in the balance sheet	[1]	3,074
Common Stocks [Member] | Financial [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		25,523
Fair value		31,577
Amount at which shown in the balance sheet	[1]	31,577
Common Stocks [Member] | Industrial [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		3,476
Fair value		4,927
Amount at which shown in the balance sheet	[1]	4,927
Common Stocks [Member] | Technology [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		1,056
Fair value		2,817
Amount at which shown in the balance sheet	[1]	2,817
Common Stocks [Member] | Funds (e.g. mutual funds, closed end funds, ETFs) [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		10,313
Fair value		9,460
Amount at which shown in the balance sheet	[1]	9,460
Common Stocks [Member] | Other [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		6,847
Fair value		8,250
Amount at which shown in the balance sheet	[1]	8,250
Commercial Mortgage Loans [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		11,782
Fair value		12,068
Amount at which shown in the balance sheet		11,782
Total Short-term and Other [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		1,000
Fair value		1,000
Amount at which shown in the balance sheet	[1]	1,000
Short-term [Member] | Certificates of Deposit [Member]
Summary of Investments, Other than Investments in Related Parties [Abstract]
Cost		1,000
Fair value		1,000
Amount at which shown in the balance sheet	[1]	$ 1,000

[1] Amounts presented above do not include investments of $59,780 classified as cash and cash equivalents in the consolidated balance sheet.