Advances - Schedule of Activity in Advances (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Advances [Roll Forward]
Beginning balance - before Allowance for Losses	$ 768,864	$ 908,829	$ 834,512	$ 1,066,448
Acquisition of advances in connection with the purchase of MSRs	0	14	4,495	14
New advances	181,567	198,549	565,284	667,577
Sales of advances	(80)	(150)	(328)	(604)
Collections of advances and other	(204,078)	(268,560)	(657,690)	(894,753)
Ending balance - before Allowance for Losses	746,273	838,682	746,273	838,682
Ending balance, net	$ 739,596	$ 832,604	$ 739,596	$ 832,604