Issuances of Common Stock - At-the-Market (ATM) Program (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
At-the-Market (ATM) Program
Gross proceeds			$ 94,076	$ 122,155
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)	31,891,256		31,891,256
Common stock | ATM Program
At-the-Market (ATM) Program
Shares of common stock issued (in shares)	1,511,149	1,706,695	1,511,149	1,706,695
Gross proceeds	$ 95,700	$ 124,200	$ 95,700	$ 124,200