Short and Long-term Funding Remaining Contractual Maturity of Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Remaining Contractual Maturity of the Agreements
Repurchase agreements	$ 91,941	$ 182,865
Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	91,941	182,865
Overnight and Continuous
Remaining Contractual Maturity of the Agreements
Repurchase agreements	91,941	182,865
Overnight and Continuous | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	91,941	182,865
Up to 30 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Up to 30 days | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
30-90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
30-90 days | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Greater than 90 days
Remaining Contractual Maturity of the Agreements
Repurchase agreements	0	0
Greater than 90 days | Agency mortgage-related securities
Remaining Contractual Maturity of the Agreements
Repurchase agreements	$ 0	$ 0