Derivative Activities - Offsetting of Derivative Assets - Derivative Liabilities, Financial Liabilities, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	$ 4,164,010	$ 1,938,264
Financial instruments	(4,141,680)	(1,935,200)
Net amount of liabilities in the consolidated balance sheet	22,330	3,064
Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,235,430	691,030
Financial instruments	(1,235,430)	(690,766)
Net amount of liabilities in the consolidated balance sheet		264
Bank of America, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	379,400	170,820
Financial instruments	(374,190)	(170,820)
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	936,172	54,326
Financial instruments	(936,172)	(54,326)
Morgan Stanley Bank
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	582,941	77,687
Financial instruments	(582,941)	(77,687)
Citibank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	655,831	14,960
Financial instruments	(653,170)	(14,960)
Net amount of liabilities in the consolidated balance sheet	2,661
BNP Paribas
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	183,880	149,675
Financial instruments	(183,880)	(149,482)
Net amount of liabilities in the consolidated balance sheet		193
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
Royal Bank of Canada
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	175,897	35,181
Financial instruments	(175,897)	(35,181)
Deutsche Bank AG
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet		741,978
Financial instruments		(741,978)
Other
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,386	1,438
Net amount of liabilities in the consolidated balance sheet	1,386	1,438
Interest rate lock commitments | Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,861	1,169
Net amount of liabilities in the consolidated balance sheet	$ 1,861	$ 1,169