Stockholders' Equity - Distribution Reinvestment Plan (Details) - USD ($) $ / shares in Units, shares in Millions		1 Months Ended	9 Months Ended	57 Months Ended	68 Months Ended
	Feb. 02, 2015	Jan. 19, 2016	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Apr. 30, 2016
Class of Stock [Line Items]
Number of shares issued (in shares)	108.6
Value of common stock issued					$ 2,000,000,000.0
Common Stock
Class of Stock [Line Items]
Number of shares issued (in shares)		173.4
Value of common stock issued		$ 1,700,000,000
Dividend Reinvestment Plan
Class of Stock [Line Items]
Share price (in dollars per share)						$ 6.25	$ 7.10	$ 8.50	$ 9.10	$ 8.63
Selling commissions or dealer manager fees paid			$ 0
Notice period served by board of directors to amend or terminate DRP (in days)			10 days
Dividend Reinvestment Plan | Common Stock
Class of Stock [Line Items]
Number of shares issued (in shares)				25.7
Value of common stock issued				$ 232,600,000
Initial Distribution Support Agreement | Dividend Reinvestment Plan
Class of Stock [Line Items]
Share price (in dollars per share)			$ 9.50	$ 9.50	$ 9.50
Follow-on Distribution Reinvestment Plan
Class of Stock [Line Items]
Share price (in dollars per share)			$ 10.20	$ 10.20	$ 10.20
Percentage of offering price			95.00%	95.00%	95.00%
Follow-on Distribution Reinvestment Plan | Dividend Reinvestment Plan
Class of Stock [Line Items]
Share price (in dollars per share)			$ 9.69	$ 9.69	$ 9.69