Distributions Paid and Payable - Distributions to Common Stockholders (Details) - $ / shares	1 Months Ended							3 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Feb. 28, 2019	Jan. 31, 2019	Mar. 31, 2018	Feb. 28, 2018	Jan. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Distributions Paid and Payable
Distributions paid per common share (in dollars per share)		$ 0.2255	$ 0.2255	$ 0.2210	$ 0.2190	$ 0.2190	$ 0.2125	$ 0.6720	$ 0.6505
Distributions payable (in dollars per share)		$ 0.226						$ 0.226
Subsequent event
Distributions Paid and Payable
Distributions paid per common share (in dollars per share)	$ 0.226