Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Notes payable secured by mortgage servicing assets	$ 1,298,067		$ 1,297,622
Unsecured Senior Notes	1,777,132		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	1,298,067		1,297,622
Unsecured senior note
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	1,777,132		1,776,219
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	796		2,588
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	(514)	$ (412)
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	796		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	1,300,813		1,302,640
Total | Unsecured senior note
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	$ 1,641,000		$ 1,790,375