Stockholders' Equity- Narrative (Details) - USD ($) $ / shares in Units, $ in Millions					4 Months Ended	12 Months Ended
	Jan. 05, 2016	Nov. 20, 2015	Mar. 31, 2015	Mar. 18, 2015	May 14, 2014	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized (in shares)						350,000,000	350,000,000
Preferred stock, shares authorized (in shares)						50,000,000	50,000,000
Convertible stock, shares authorized (in shares)						1,000	1,000
Number of shares of common stock issued in offering (in shares)						26,700,000
Common stock, shares outstanding (in shares)						24,646,494	25,218,770
Number of shares issued through distribution reinvestment (in shares)						2,200,000
Common stock redeemed (in shares)						2,100,000
Convertible stock, shares outstanding (in shares)						1,000	1,000
Share repurchase program, cash available for redemption					$ 1.0	$ 10.0
Share redemption program, annual limitation, percentage of weighted average shares outstanding						5.00%
Special distributions declared on common stock (in dollars per share)		$ 1.50		$ 1.00
Total distributions paid to stockholders	$ 38.4		$ 25.7
Percentage of real estate investment trust taxable income						90.00%
Minimum
Class of Stock [Line Items]
Share redemption program, redemption price, percentage of share price						80.00%
Stock repurchase program period of notice to be provided to stockholders for application of new redemption price						30 days
Maximum
Class of Stock [Line Items]
Share redemption program, redemption price, percentage of share price						90.00%
Convertible Stock
Class of Stock [Line Items]
Cumulative, non-compounded, annual return for shares for automatic conversion of convertible stock						10.00%
Average period considered for determination of aggregate market value of common stock						30 days
Percentage of excess of enterprise value plus the aggregate value of distributions paid to date on outstanding shares of common stock over aggregate issue price of outstanding shares for determination of conversion price						20.00%
Cumulative, non-compounded, annual return on issue price added to issue price for determination of conversion price						10.00%
Percentage of excess of enterprise value plus the aggregate value of distributions paid to date on outstanding shares of common stock over aggregate issue price of outstanding shares for determination of conversion price						15.00%
Cumulative, non-compounded, annual return on issue price for determination of conversion price						6.00%