Fair Value - Measurement Basis, Nonrecurring (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 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	$ 1,793,972		$ 1,793,972		$ 1,297,622
Unsecured Senior Notes	1,778,988		1,778,988		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	1,793,972		1,793,972		1,297,622
Unsecured senior note
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	1,778,988		1,778,988		1,776,219
Nonrecurring basis
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	911		911		2,588
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Real estate acquired in settlement of loans	(131)	$ (284)	(838)	$ (912)
Nonrecurring basis | Level 3
Financial statement items measured at fair value on a nonrecurring basis
Real estate acquired in settlement of loans	911		911		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	1,717,125		1,717,125		1,302,640
Total | Unsecured senior note
Total gains (losses) on assets measured at estimated fair values on a nonrecurring basis
Unsecured Senior Notes	$ 1,371,500		$ 1,371,500		$ 1,790,375