Subsequent Events (Narrative) (Details) - USD ($)	Oct. 30, 2020	Oct. 09, 2020	Nov. 05, 2020	Nov. 02, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2013
Subsequent Event [Line Items]
Financing agreements ($4,080,461 and $0 held at fair value, respectively)					$ 4,851,121,000	$ 10,031,606,000
Stock repurchase program, authorized amount							$ 10,000,000
Number of remaining shares authorized to be repurchased under the Repurchase Program (in shares)					6,616,355
Common stock, shares outstanding (in shares)					453,333,000	452,369,000
Subsequent Event
Subsequent Event [Line Items]
Repayments of debt	$ 81,250,000	$ 400,000,000
Stock repurchase program, authorized amount				$ 250,000,000
Subsequent Event | Non-QM Loans [Member]
Subsequent Event [Line Items]
Financing agreements ($4,080,461 and $0 held at fair value, respectively)			$ 570,000,000
Cash			$ 125,100,000