Derivative Instruments, Offsetting Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets or liabilities	$ 1,602,589	$ 1,666,881
Gross amounts offset in the consolidated balance sheet	(181)	0
Net amounts of liabilities presented in the consolidated balance sheet	1,602,408	1,666,881
Gross amounts not offset in the consolidated balance sheet in financial instruments	(1,594,910)	(1,637,713)
Gross amounts not offset in the consolidated balance sheet in cash collateral received (pledged)	(7,498)	(29,168)
Net amount	0	0
Repurchase Agreements [Member]
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets or liabilities	1,598,592	1,666,537
Gross amounts offset in the consolidated balance sheet	0	0
Net amounts of liabilities presented in the consolidated balance sheet	1,598,592	1,666,537
Gross amounts not offset in the consolidated balance sheet in financial instruments	(1,591,094)	(1,637,922)
Gross amounts not offset in the consolidated balance sheet in cash collateral received (pledged)	(7,498)	(28,615)
Net amount	0	0
Interest Rate Swaps [Member]
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets or liabilities	3,816	342
Gross amounts offset in the consolidated balance sheet	0	0
Net amounts of liabilities presented in the consolidated balance sheet	3,816	342
Gross amounts not offset in the consolidated balance sheet in financial instruments	(3,816)	32
Gross amounts not offset in the consolidated balance sheet in cash collateral received (pledged)	0	(374)
Net amount	0	0
TBAs [Member]
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets or liabilities	181
Gross amounts offset in the consolidated balance sheet	(181)
Net amounts of liabilities presented in the consolidated balance sheet	0
Gross amounts not offset in the consolidated balance sheet in financial instruments	0
Gross amounts not offset in the consolidated balance sheet in cash collateral received (pledged)	0
Net amount	$ 0
Treasury Futures [Member]
Offsetting Derivative Liabilities [Abstract]
Gross amounts of recognized assets or liabilities		2
Gross amounts offset in the consolidated balance sheet		0
Net amounts of liabilities presented in the consolidated balance sheet		2
Gross amounts not offset in the consolidated balance sheet in financial instruments		177
Gross amounts not offset in the consolidated balance sheet in cash collateral received (pledged)		(179)
Net amount		$ 0

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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