Segment Reporting - Adjusted Pretax Operating Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 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	$ (4,487)	$ (236)	$ (3,997)	$ 5,349
Pretax income	188,123	182,676	386,772	386,687
Corporate, Non-Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
All Other adjusted pretax operating income (loss)	(6,080)	(13,724)	(13,113)	(28,560)
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	(4,438)	(331)	(4,331)	5,174
Amortization and impairment of goodwill and other acquired intangible assets	0	(1,370)	0	(2,741)
Impairment of other long-lived assets and other non-operating items	(122)	2	(4,397)	16
Mortgage Insurance revenues
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Allocated corporate operating expenses	43,197	37,081	77,706	71,910
Direct depreciation expense	2,069	2,045	3,992	4,169
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)	$ 198,763	$ 198,099	$ 408,613	$ 412,798