Summary of Significant Accounting Policies - Intangible Assets - Schedule of Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill	$ 46,062	$ 46,062
Indefinite-lived intangibles - state insurance licenses	7,500	7,500
Definite-lived intangibles, net of accumulated amortization of $4,015 at 6/30/21 and $3,878 at 12/31/20	20	157
Total intangibles	7,520	7,657
Total goodwill and intangibles	53,582	53,719
Surety
Business Acquisition [Line Items]
Goodwill	40,816	40,816
Casualty
Business Acquisition [Line Items]
Goodwill	$ 5,246	$ 5,246