Summary of Significant Accounting Policies - Narrative - Distribution Policy (Details) - $ / shares			3 Months Ended								12 Months Ended
	May 02, 2018	Mar. 13, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Distributions declared per common share (in dollars per share)			$ 0.140	$ 0.140	$ 1.153	$ 0.177	$ 0.181	$ 0.181	$ 0.179	$ 0.177	$ 1.610	$ 0.718
Common share, distribution rate per share per day, declared (in dollars per share)		$ 0.00151890410958904		$ 0.001519	$ 0.001683	$ 0.001964
Dividend Paid [Member]
Related Party Transaction [Line Items]
Distributions declared per common share (in dollars per share)	$ 1.00