Schedule I-Summary of Investments-Other Than Investments in Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments-Other Than Investments in Related Parties
Amortized Cost	$ 1,629,538	$ 1,275,972
Fair Value	1,615,102	1,276,634
Amount at which shown in the Balance Sheet	1,615,102
Residential and commercial mortgage securities
Investments-Other Than Investments in Related Parties
Amortized Cost	68,430	56,380
Fair Value	68,336	55,356
Asset-backed securities
Investments-Other Than Investments in Related Parties
Amortized Cost	127,359	127,919
Fair Value	127,172	126,629
Fixed maturities
Investments-Other Than Investments in Related Parties
Amortized Cost	1,497,186	1,189,978
Fair Value	1,482,754
Amount at which shown in the Balance Sheet	1,482,754
Fixed maturities \| United States Government and government agencies and authorities
Investments-Other Than Investments in Related Parties
Amortized Cost	509,507
Fair Value	496,565
Amount at which shown in the Balance Sheet	496,565
Fixed maturities \| States, municipalities and political subdivisions
Investments-Other Than Investments in Related Parties
Amortized Cost	334,048
Fair Value	334,324
Amount at which shown in the Balance Sheet	334,324
Fixed maturities \| Residential and commercial mortgage securities
Investments-Other Than Investments in Related Parties
Amortized Cost	68,430
Fair Value	68,336
Amount at which shown in the Balance Sheet	68,336
Fixed maturities \| Asset-backed securities
Investments-Other Than Investments in Related Parties
Amortized Cost	127,359
Fair Value	127,172
Amount at which shown in the Balance Sheet	127,172
Fixed maturities \| All other corporate bonds
Investments-Other Than Investments in Related Parties
Amortized Cost	457,842
Fair Value	456,357
Amount at which shown in the Balance Sheet	456,357
Short-term investments
Investments-Other Than Investments in Related Parties
Amortized Cost	132,352	$ 85,994
Fair Value	132,348
Amount at which shown in the Balance Sheet	$ 132,348

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 7
-Subparagraph (SX 210.12-15)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611379-123010

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