Derivative Financial Instruments - Offsetting of Derivative Assets - Derivative Liabilities, Financial Liabilities, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	$ 7,291,583	$ 4,164,010
Financial instruments	(7,267,046)	(4,141,680)
Net amount of liabilities in the consolidated balance sheet	24,537	22,330
Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	3,613,132	1,235,430
Financial instruments	(3,607,746)	(1,235,430)
Net amount of liabilities in the consolidated balance sheet	5,386
Barclays
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,648
Net amount of liabilities in the consolidated balance sheet	1,648
Bank of America, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	767,391	379,400
Financial instruments	(767,391)	(374,190)
Net amount of liabilities in the consolidated balance sheet		5,210
JP Morgan
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	741,341	936,172
Financial instruments	(741,341)	(936,172)
Morgan Stanley Bank
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	784,434	582,941
Financial instruments	(784,434)	(582,941)
BNP Paribas
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	370,013	183,880
Financial instruments	(370,013)	(183,880)
Royal Bank of Canada
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	363,193	175,897
Financial instruments	(363,193)	(175,897)
Citibank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	637,347	655,831
Financial instruments	(632,928)	(653,170)
Net amount of liabilities in the consolidated balance sheet	4,419	2,661
Wells Fargo Bank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet		11,212
Net amount of liabilities in the consolidated balance sheet		11,212
Mizuho Securities
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,366
Net amount of liabilities in the consolidated balance sheet	2,366
Federal National Mortgage Association
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	5,755
Net amount of liabilities in the consolidated balance sheet	5,755
Other
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,257	1,386
Net amount of liabilities in the consolidated balance sheet	2,257	1,386
Interest rate lock commitments
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,706	1,861
Net amount of liabilities in the consolidated balance sheet	$ 2,706	$ 1,861