Financing Agreements (Counterparty for Repurchase Agreement) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) counterparty	Dec. 31, 2019 counterparty
Repurchase agreements counterparty risk
Number of counterparties | counterparty	8	28
Threshold of stockholders' equity at risk with single counterparty to repurchase agreements or linked transactions (greater than) (percent)	5.00%
Amounts at risk exceeding equity	5.00%
Barclays Bank
Repurchase agreements counterparty risk
Amount at Risk	$ 750,922
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	29.30%
Credit Suisse
Repurchase agreements counterparty risk
Amount at Risk	$ 574,835
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	22.40%
Wells Fargo
Repurchase agreements counterparty risk
Amount at Risk	$ 349,825
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	13.60%
Goldman Sachs
Repurchase agreements counterparty risk
Amount at Risk	$ 173,266
Weighted  Average Months  to Repricing for Repurchase Agreements	3 months
Percent of Stockholders’ Equity	6.80%
Goldman Sachs Lending Partners
Repurchase agreements counterparty risk
Amount at Risk	$ 20,600
Goldman Sachs Bank USA
Repurchase agreements counterparty risk
Amount at Risk	152,700
Athene
Repurchase agreements counterparty risk
Amount at Risk	$ 144,245
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	5.60%