Underwriting Information - Gross Written Premiums by Insurance Subsidiary (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Gross written premiums
Amount	$ 152,332	$ 102,967	$ 385,267	$ 258,268
% of GWP	100.00%	100.00%	100.00%	100.00%
PSIC
Gross written premiums
Amount	$ 110,875	$ 93,987	$ 285,991	$ 249,288
% of GWP	72.80%	91.30%	74.20%	96.50%
PESIC
Gross written premiums
Amount	$ 41,457	$ 8,980	$ 99,276	$ 8,980
% of GWP	27.20%	8.70%	25.80%	3.50%