Investments - Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Net Investment Income
Investment income	$ 32,230	$ 36,305	$ 63,842	$ 70,777
Investment expenses	(1,055)	(1,174)	(2,424)	(2,201)
Net investment income	31,175	35,131	61,418	68,576
Reciprocal Exchanges
Net Investment Income
Net investment income	2,012	2,124	4,195	4,294
NGHC, excluding Reciprocal Exchanges
Net Investment Income
Net investment income	29,163	33,007	57,223	64,282
Cash and short-term investments
Net Investment Income
Investment Income	30	847	308	2,344
Debt securities, available-for-sale
Net Investment Income
Investment Income	30,491	30,725	62,593	60,192
Other, net
Net Investment Income
Investment Income, Net	1,709	4,733	941	8,241
Other, net \| Related Parties
Net Investment Income
Investment Income, Net	$ 1,042	$ 1,919	$ (1,483)	$ 2,173

Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-Section S99
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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