Segment Reporting - Adjusted Pretax Operating Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net gains (losses) on investments and other financial instruments	$ (10,114)	$ 10,241	$ (80,733)
Pretax income	771,290	767,487	952,779
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Mortgage insurance adjusted pretax operating income	827,363	829,824	1,131,943
Corporate, Non-Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
All Other adjusted pretax operating income (loss)	(24,358)	(43,397)	(79,226)
Net gains (losses) on investments and other financial instruments	(5,798)	814	47
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	(4,316)	9,427	(80,780)
Amortization and impairment of goodwill and other acquired intangible assets	0	(15,285)	(4,308)
Impairment of other long-lived assets and other non-operating items	(27,399)	(13,082)	(14,850)
Mortgage Insurance revenues | Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Mortgage insurance adjusted pretax operating income	827,363	829,824	1,131,943
Net gains (losses) on investments and other financial instruments	$ 0	$ 0	$ 0