Derivative Financial Instruments - Offsetting of Derivative Assets - Derivative Liabilities, Financial Liabilities, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	$ 10,925,234	$ 9,706,633
Financial instruments	(10,856,677)	(9,663,995)
Net amount of liabilities in the consolidated balance sheet	68,557	42,638
Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,824,198	3,947,752
Financial instruments	(2,805,703)	(3,943,149)
Net amount of liabilities in the consolidated balance sheet	18,495	4,603
JP Morgan
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,841,831	2,752,279
Financial instruments	(2,841,831)	(2,752,279)
Bank of America, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,317,580	634,523
Financial instruments	(1,317,580)	(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	738,528	596,729
Financial instruments	(730,340)	(596,729)
Net amount of liabilities in the consolidated balance sheet	8,188
Citibank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	787,322	505,625
Financial instruments	(787,322)	(505,625)
Royal Bank of Canada
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	434,487	406,348
Financial instruments	(434,487)	(406,348)
BNP Paribas
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	308,754	337,823
Financial instruments	(308,754)	(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	562,172	331,546
Financial instruments	(562,172)	(331,546)
Wells Fargo Bank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	173,051	169,085
Financial instruments	(173,051)	(165,224)
Net amount of liabilities in the consolidated balance sheet		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	8,107	6,491
Net amount of liabilities in the consolidated balance sheet	8,107	6,491
Goldman Sachs
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	895,437
Financial instruments	(895,437)
Nomura Securities International, Inc.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,264
Net amount of liabilities in the consolidated balance sheet	2,264
Mitsubishi UFJ Securities
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	3,305
Net amount of liabilities in the consolidated balance sheet	3,305
Other
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	3,215	2,569
Net amount of liabilities in the consolidated balance sheet	3,215	2,569
Interest rate lock commitments
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	24,983	2,935
Net amount of liabilities in the consolidated balance sheet	$ 24,983	$ 2,935