Derivative Activities - Offsetting of Derivative Assets - Derivative Liabilities, Financial Liabilities, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	$ 1,938,264	$ 2,386,662
Financial instruments	(1,935,200)	(2,380,866)
Net amount of liabilities in the consolidated balance sheet	3,064	5,796
Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	691,030	1,010,562
Financial instruments	(690,766)	(1,010,320)
Net amount of liabilities in the consolidated balance sheet	264	242
Bank of America, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	170,820	406,787
Financial instruments	(170,820)	(406,355)
Net amount of liabilities in the consolidated balance sheet		432
Deutsche Bank AG
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	741,978	593,864
Financial instruments	(741,978)	(593,864)
Barclays
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet		6,387
Financial instruments		(6,387)
Royal Bank of Canada
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	35,181	24,835
Financial instruments	(35,181)	(23,752)
Net amount of liabilities in the consolidated balance sheet		1,083
JP Morgan
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	54,326	90,442
Financial instruments	(54,326)	(90,442)
Morgan Stanley Bank
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	77,687	139,491
Financial instruments	(77,687)	(138,983)
Net amount of liabilities in the consolidated balance sheet		508
Citibank, N.A.
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	14,960	23,010
Financial instruments	(14,960)	(23,010)
BNP Paribas
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	149,675	87,753
Financial instruments	(149,482)	(87,753)
Net amount of liabilities in the consolidated balance sheet	193
Other
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,438	1,791
Net amount of liabilities in the consolidated balance sheet	1,438	1,791
Interest rate lock commitments | Credit Suisse First Boston Mortgage Capital LLC
Derivative liabilities:
Net amounts of liabilities presented in the consolidated balance sheet	1,169	1,740
Net amount of liabilities in the consolidated balance sheet	$ 1,169	$ 1,740