Financing Agreements (Counterparty for Repurchase Agreement) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) counterparty	Dec. 31, 2019 counterparty
Repurchase agreements counterparty risk
Number of counterparties | counterparty	7	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	$ 505,580
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	20.00%
Credit Suisse
Repurchase agreements counterparty risk
Amount at Risk	$ 438,336
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	17.40%
Wells Fargo
Repurchase agreements counterparty risk
Amount at Risk	$ 337,769
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	13.40%
Goldman Sachs
Repurchase agreements counterparty risk
Amount at Risk	$ 187,122
Weighted  Average Months  to Repricing for Repurchase Agreements	0 months
Percent of Stockholders’ Equity	7.40%
Goldman Sachs Lending Partners
Repurchase agreements counterparty risk
Amount at Risk	$ 25,400
Goldman Sachs Bank USA
Repurchase agreements counterparty risk
Amount at Risk	161,700
Athene
Repurchase agreements counterparty risk
Amount at Risk	$ 133,286
Weighted  Average Months  to Repricing for Repurchase Agreements	1 month
Percent of Stockholders’ Equity	5.30%