Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	$ 1,942,646	$ 1,297,622
Unsecured Senior Notes	1,779,920	1,776,219
Term Notes
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	1,794,475	1,297,622
Unsecured senior note
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	1,779,920	1,776,219
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	1,850	2,588
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	523	799	$ 814
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	1,850	2,588
Total | Term Notes
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	1,677,476	1,302,640
Total | Unsecured senior note
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	$ 1,550,750	$ 1,790,375