Deferred Acquisition Costs (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Movement Analysis of Deferred Policy Acquisition Costs
Balance, beginning of the period	$ 263,523	$ 251,408
Additions	498,474	426,792
Amortization	(477,034)	(410,541)
Change in DAC	21,440	16,251
Balance, end of the period	284,963	267,659
Reciprocal Exchanges
Movement Analysis of Deferred Policy Acquisition Costs
Balance, end of the period	18,507	23,113
NGHC, excluding Reciprocal Exchanges
Movement Analysis of Deferred Policy Acquisition Costs
Balance, end of the period	266,456	244,546
Property and Casualty
Movement Analysis of Deferred Policy Acquisition Costs
Balance, beginning of the period	239,293	226,188
Additions	479,934	385,570
Amortization	(461,933)	(372,741)
Change in DAC	18,001	12,829
Balance, end of the period	257,294	239,017
Property and Casualty | Reciprocal Exchanges
Movement Analysis of Deferred Policy Acquisition Costs
Balance, end of the period	18,507	23,113
Property and Casualty | NGHC, excluding Reciprocal Exchanges
Movement Analysis of Deferred Policy Acquisition Costs
Balance, end of the period	238,787	215,904
Accident and Health
Movement Analysis of Deferred Policy Acquisition Costs
Balance, beginning of the period	24,230	25,220
Additions	18,540	41,222
Amortization	(15,101)	(37,800)
Change in DAC	3,439	3,422
Balance, end of the period	27,669	28,642
Accident and Health | Reciprocal Exchanges
Movement Analysis of Deferred Policy Acquisition Costs
Balance, end of the period	0	0
Accident and Health | NGHC, excluding Reciprocal Exchanges
Movement Analysis of Deferred Policy Acquisition Costs
Balance, end of the period	$ 27,669	$ 28,642