Segment and Other Operating Information - Premiums and Other Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting [Abstract]
Premiums and contract revenues	$ 54,339	$ 56,172	$ 109,323	$ 113,645
Net investment income (loss)	55,474	156,544	125,198	322,619
Other revenues	5,578	6,034	11,375	11,448
Realized gains on investments	1,766	3,415	5,560	4,831
Total revenues	$ 117,157	$ 222,165	$ 251,456	$ 452,543