Organization and Business - ATM Program (Details) - USD ($)		1 Months Ended		3 Months Ended			9 Months Ended
	Aug. 05, 2016	Jul. 31, 2017	Mar. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Oct. 31, 2017
Class of Stock [Line Items]
Common shares sold (in shares)		21,500,000	17,250,000
Net proceeds		$ 420,700,000	$ 300,800,000
2016 ATM Program
Class of Stock [Line Items]
Common shares sold (in shares)				0	4,150,000	0	4,150,000
Weighted average price				$ 0	$ 20.07	$ 0	$ 20.07
Net proceeds				$ 0	$ 82,440,000	$ 0	$ 82,440,000
Subsequent Event
Class of Stock [Line Items]
Sale of stock, remaining authorized amount								$ 216,700,000
Maximum | Private Placement | 2016 ATM Program
Class of Stock [Line Items]
Aggregate offering price of common stock	$ 300,000,000