Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 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	$ 2,471,930		$ 1,942,646
Unsecured Senior Notes	1,780,833		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	2,471,930		1,794,475
Unsecured senior notes.
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	1,780,833		1,779,920
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	2,324		1,850
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	(558)	$ (514)
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	2,324		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	2,466,450		1,677,476
Total | Unsecured senior notes.
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	$ 1,490,375		$ 1,550,750