Losses and LAE - Mortgage Insurance Reserve for Losses and LAE Rollforward (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Loss reserve [Roll Forward]
Balance at beginning of period	$ 370,148
Deduct: Paid claims and LAE related to:
Balance at end of period	363,225
Mortgage Insurance revenues
Loss reserve [Roll Forward]
Balance at beginning of period	364,923	$ 420,955
Less: Reinsurance recoverables	25,074	24,727
Balance at beginning of period, net of reinsurance recoverables	325,244	338,569	$ 339,849	$ 396,228
Add: Losses and LAE incurred in respect of default notices reported and unreported in:
Current year	151,497	130,740
Prior years	(153,806)	(177,483)
Total incurred	(2,309)	(46,743)
Deduct: Paid claims and LAE related to:
Current year	359	204
Prior years	11,937	10,712
Total paid	12,296	10,916
Balance at end of period, net of reinsurance recoverables	325,244	338,569
Add: Reinsurance recoverables	31,710	23,269
Balance at end of period	$ 356,954	$ 361,838