Segment Reporting - Adjusted Pretax Operating Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net gains (losses) on investments and other financial instruments		$ (4,852)	$ (4,487)	$ (5,575)	$ (3,997)
Pretax income		175,013	188,123	363,453	386,772
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Mortgage Insurance adjusted pretax operating income		189,522	198,763	383,815	408,613
Corporate, Non-Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
All Other adjusted pretax operating income (loss)		(16,361)	(6,080)	(19,820)	(13,113)
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	[1]	1,852	(4,438)	(158)	(4,331)
Impairment of other long-lived assets and other non-operating items	[2]	0	(122)	(384)	(4,397)
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		189,522	198,763	383,815	408,613
Allocated corporate operating expenses	[3]	42,328	43,197	77,451	77,706
Direct depreciation expense		$ 1,916	$ 2,069	$ 3,856	$ 3,992

[1] Does not include net gains (losses) on investments and other financial instruments that are attributable to our Mortgage Conduit business, which are included in All Other adjusted pretax operating income (loss).

[2] The non-operating item for the six months ended June 30, 2024, primarily relates to a loss on extinguishment of debt.

[3] Includes immaterial allocated depreciation expense.