Derivative Financial Instruments - Offsetting of Derivative Assets - Derivative Liabilities, Financial Liabilities, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	$ 4,489,947	$ 4,164,010
Financial instruments	(4,446,795)	(4,141,680)
Net amount of liabilities in the consolidated balance sheet	43,152	22,330
Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,552,669	1,235,430
Financial instruments	(1,533,516)	(1,235,430)
Net amount of liabilities in the consolidated balance sheet	19,153
Bank of America, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	654,788	379,400
Financial instruments	(643,834)	(374,190)
Net amount of liabilities in the consolidated balance sheet	10,954	5,210
JP Morgan
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	870,965	936,172
Financial instruments	(870,965)	(936,172)
Morgan Stanley Bank
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	296,497	582,941
Financial instruments	(293,813)	(582,941)
Net amount of liabilities in the consolidated balance sheet	2,684
BNP Paribas
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	196,791	183,880
Financial instruments	(196,433)	(183,880)
Net amount of liabilities in the consolidated balance sheet	358
Royal Bank of Canada
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	250,919	175,897
Financial instruments	(250,919)	(175,897)
Citibank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	657,315	655,831
Financial instruments	(657,315)	(653,170)
Net amount of liabilities in the consolidated balance sheet		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	1,396
Net amount of liabilities in the consolidated balance sheet	1,396
Federal National Mortgage Association
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	5,674
Net amount of liabilities in the consolidated balance sheet	5,674
Other
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	506	1,386
Net amount of liabilities in the consolidated balance sheet	506	1,386
Interest rate lock commitments
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	2,427	1,861
Net amount of liabilities in the consolidated balance sheet	$ 2,427	$ 1,861