Segment Reporting - Adjusted Pretax Operating Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net gains (losses) on investments and other financial instruments	$ 2,174	$ (8,555)	$ (1,823)	$ (3,206)
Pretax income	195,392	200,983	582,164	587,670
Corporate, Non-Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
All Other adjusted pretax operating income (loss)	(4,875)	(8,774)	(17,988)	(37,334)
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net gains (losses) on investments and other financial instruments	6,785	(8,838)	2,454	(3,664)
Amortization and impairment of goodwill and other acquired intangible assets	0	(1,371)	0	(4,112)
Impairment of other long-lived assets and other non-operating items	(10,061)	737	(14,458)	753
Mortgage Insurance revenues
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Allocated corporate operating expenses	32,533	31,744	110,239	103,654
Direct depreciation expense	2,003	1,995	5,995	6,164
Mortgage Insurance revenues | Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
All Other adjusted pretax operating income (loss)	$ 203,543	$ 219,229	$ 612,156	$ 632,027