Stockholders' Equity - Additional Information (Details) - USD ($)									3 Months Ended
	Mar. 31, 2019	Feb. 21, 2019	Feb. 20, 2019	Apr. 30, 2018	Feb. 15, 2018	Mar. 16, 2017	Aug. 11, 2016	Jun. 15, 2016	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Nov. 14, 2018	Sep. 30, 2018	Dec. 31, 2017
Class Of Stock [Line Items]
Common stock, shares, issued	23,643,277								23,643,277		23,499,635
Common stock, shares, outstanding	23,643,277								23,643,277		23,499,635
Common stock, par value	$ 0.01							$ 0.01	$ 0.01		$ 0.01	$ 0.01
Share repurchase program, authorized amount				$ 40,000,000				$ 30,000,000
Stock repurchase program, expiration date				Jun. 15, 2020				Jun. 15, 2018
Stock repurchase program period in force				2 years				2 years
Share repurchase program, treasury stock shares	737,458								0
Share repurchase program, treasury stock, value	$ 16,694,000									$ 5,058,000
Share repurchase program, treasury stock, per share	$ 22.64
Common Stock
Class Of Stock [Line Items]
Common stock, shares, issued	23,643,277								23,643,277	20,926,355	23,499,635			21,049,565
At-the-Market Offering | Common Stock
Class Of Stock [Line Items]
Common stock, par value			$ 0.01
Maximum | At-the-Market Offering | Common Stock
Class Of Stock [Line Items]
Aggregate sale price of common stock			$ 100,000,000
Restricted Stock Units
Class Of Stock [Line Items]
Restricted stock units, granted									186,662
2016 LTIP
Class Of Stock [Line Items]
Common stock, shares, issued									143,642
Common stock, shares, issued	384,410								384,410
Common stock, par value								$ 0.01
Number of shares authorized to issue								2,100,000
2016 LTIP | Restricted Stock Units
Class Of Stock [Line Items]
Equity-based compensation expense									$ 1,200,000	$ 900,000
Dividends earned on restricted stock units													$ 600,000
2016 LTIP | Restricted Stock Units | Director
Class Of Stock [Line Items]
Vesting period description									annually
2016 LTIP | Restricted Stock Units | Directors and Officers
Class Of Stock [Line Items]
Restricted stock units, granted						219,802	209,797
2016 LTIP | Restricted Stock Units | Directors, Officers, Employees and Certain Key Employees of Adviser
Class Of Stock [Line Items]
Restricted stock units, granted		186,662			275,795
2016 LTIP | Restricted Stock Units | Minimum | Officers, Employees and Certain Key Employees of Adviser
Class Of Stock [Line Items]
Restricted stock units, vesting period									3 years
2016 LTIP | Restricted Stock Units | Maximum | Officers, Employees and Certain Key Employees of Adviser
Class Of Stock [Line Items]
Restricted stock units, vesting period									5 years