Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	$ 2,472,726		$ 2,472,726		$ 1,942,646
Unsecured Senior Notes	1,781,756		1,781,756		1,779,920
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	2,472,726		2,472,726		1,794,475
Unsecured senior notes.
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	1,781,756		1,781,756		1,779,920
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	2,873		2,873		1,850
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	(740)	$ (326)	(900)	$ (740)
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	2,873		2,873		1,850
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	2,469,563		2,469,563		1,677,476
Total | Unsecured senior notes.
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	$ 1,551,467		$ 1,551,467		$ 1,550,750