Issuances of Common Stock - At-the-Market (ATM) Program (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
At-the-Market (ATM) Program
Gross proceeds			$ 442,157	$ 689,641
ATM Program
At-the-Market (ATM) Program
At-the-Market equity distribution program, authorized shares (in shares)	33,402,405		33,402,405
Shares remaining for future issuance (in shares)	26,354,637		26,354,637
Common stock | ATM Program
At-the-Market (ATM) Program
Shares of common stock issued (in shares)	5,536,619	7,663,383	7,047,768	9,370,078
Gross proceeds	$ 346,500	$ 570,300	$ 442,200	$ 694,400