Commitments - Schedule of Activity Related to HMBS Repurchases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) security
Schedule Of Repurchases Activity [Roll Forward]
Beginning balance, repurchase securities, number | security	262
Additions, repurchase securities, number | security	322
Recoveries, net, repurchase securities, number | security	(264)
Transfers, repurchase securities, number | security	0
Change in value, repurchase securities, number | security	0
Ending balance, repurchase securities, number | security	320
Beginning balance, repurchase securities, value | $	$ 16,880
Additions, repurchase securities, value | $	44,188
Recoveries, repurchase securities, value | $	(22,934)
Transfers, repurchase securities, value | $	0
Change in value, repurchase securities, value | $	(2,441)
Ending balance, repurchase securities, value | $	$ 35,693
Active
Schedule Of Repurchases Activity [Roll Forward]
Beginning balance, repurchase securities, number | security	10
Additions, repurchase securities, number | security	81
Recoveries, net, repurchase securities, number | security	(30)
Transfers, repurchase securities, number | security	1
Change in value, repurchase securities, number | security	0
Ending balance, repurchase securities, number | security	62
Beginning balance, repurchase securities, value | $	$ 2,047
Additions, repurchase securities, value | $	19,671
Recoveries, repurchase securities, value | $	(10,414)
Transfers, repurchase securities, value | $	(785)
Change in value, repurchase securities, value | $	27
Ending balance, repurchase securities, value | $	$ 10,546
Inactive
Schedule Of Repurchases Activity [Roll Forward]
Beginning balance, repurchase securities, number | security	252
Additions, repurchase securities, number | security	241
Recoveries, net, repurchase securities, number | security	(234)
Transfers, repurchase securities, number | security	(1)
Change in value, repurchase securities, number | security	0
Ending balance, repurchase securities, number | security	258
Beginning balance, repurchase securities, value | $	$ 14,833
Additions, repurchase securities, value | $	24,517
Recoveries, repurchase securities, value | $	(12,520)
Transfers, repurchase securities, value | $	785
Change in value, repurchase securities, value | $	(2,468)
Ending balance, repurchase securities, value | $	$ 25,147