Derivative Financial Instruments - Offsetting of Derivative Assets - Derivative Liabilities, Financial Liabilities, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	$ 8,306,161	$ 9,706,633
Financial instruments	(8,262,251)	(9,663,995)
Net amount of liabilities in the consolidated balance sheet	43,910	42,638
Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,214,762	2,752,279
Financial instruments	(2,214,762)	(2,752,279)
JP Morgan
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,873,730	3,947,752
Financial instruments	(1,866,023)	(3,943,149)
Net amount of liabilities in the consolidated balance sheet	7,707	4,603
Bank of America, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,053,871	634,523
Financial instruments	(1,053,871)	(626,550)
Net amount of liabilities in the consolidated balance sheet		7,973
Barclays
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	348,272	596,729
Financial instruments	(348,272)	(596,729)
Citibank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	204,515	505,625
Financial instruments	(193,628)	(505,625)
Net amount of liabilities in the consolidated balance sheet	10,887
Royal Bank of Canada
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	728,898	406,348
Financial instruments	(728,898)	(406,348)
BNP Paribas
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	372,377	337,823
Financial instruments	(372,377)	(336,545)
Net amount of liabilities in the consolidated balance sheet		1,278
Morgan Stanley Bank
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	353,729	331,546
Financial instruments	(353,729)	(331,546)
Wells Fargo Bank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	349,852	169,085
Financial instruments	(342,509)	(165,224)
Net amount of liabilities in the consolidated balance sheet	7,343	3,861
Federal National Mortgage Association
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet		12,928
Net amount of liabilities in the consolidated balance sheet		12,928
Mizuho Securities
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	14,225	6,491
Net amount of liabilities in the consolidated balance sheet	14,225	6,491
Goldman Sachs
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	788,182
Financial instruments	(788,182)
Other
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	3,230	2,569
Net amount of liabilities in the consolidated balance sheet	3,230	2,569
Interest rate lock commitments
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	518	2,935
Net amount of liabilities in the consolidated balance sheet	$ 518	$ 2,935