Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	$ 1,723,632		$ 1,723,632		$ 1,873,415
Unsecured Senior Notes	3,162,239		3,162,239		2,519,651
Term Notes and Term Loans
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	1,723,632		1,723,632		1,724,290
Unsecured senior notes.
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	3,162,239		3,162,239		2,519,651
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	6,687		6,687		2,669
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	(1,758)	$ (494)	(2,804)	$ (791)
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	6,687		6,687		2,669
Total | Term Notes and Term Loans
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	1,742,421		1,742,421		1,730,000
Total | Unsecured senior notes.
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	$ 3,235,284		$ 3,235,284		$ 2,467,750