Issuances of Common Stock - At-the-Market (ATM) Programs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
At-the-Market (ATM) Programs
Gross proceeds	$ 1,264,518	$ 1,125,364	$ 621,697
ATM Program
At-the-Market (ATM) Programs
Common shares for future issuance (in shares)	33,402,405
Common stock | ATM Program
At-the-Market (ATM) Programs
Shares of common stock issued (in shares)	17,051,456	19,138,610	10,914,088
Gross proceeds	$ 1,274,500	$ 1,125,400	$ 621,700