Segment Reporting - Segment and Revenue Information (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]
Total revenues		$ 318,004	$ 321,147	$ 636,118	$ 640,565
Provision for losses		12,097	(1,745)	27,264	(8,779)
Policy acquisition costs		7,205	6,522	13,593	13,316
Interest expense		25,874	27,064	48,373	56,110
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Adjusted pretax operating income		189,522	198,763	383,815	408,613
Operating Segments | Mortgage Insurance revenues
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total revenues		288,316	285,983	572,614	571,006
Provision for losses		11,954	(1,769)	27,294	(8,655)
Policy acquisition costs		7,205	6,522	13,593	13,316
Direct other operating expenses		19,874	17,157	36,441	34,427
Allocated corporate operating expenses	[1]	42,328	43,197	77,451	77,706
Interest expense		17,428	21,957	33,917	45,290
Other segment items		5	156	103	309
Adjusted pretax operating income		189,522	198,763	383,815	408,613
Direct depreciation expense		$ 1,916	$ 2,069	$ 3,856	$ 3,992
Loss Ratio	[2]	5.10%	(0.80%)	5.80%	(1.80%)
Expense Ratio	[3]	29.70%	28.50%	27.30%	26.80%

[1] Includes immaterial allocated depreciation expense.

[2] Calculated as provision for losses expressed as a percentage of net premiums earned.

[3] Calculated as operating expenses (which consist of policy acquisition costs, direct other operating expenses and allocated corporate operating expenses) expressed as a percentage of net premiums earned.