Stockholders' Equity - Additional Information (Details) - USD ($)													3 Months Ended		6 Months Ended		12 Months Ended	69 Months Ended
	May 11, 2020	Mar. 13, 2020	Mar. 04, 2020	Feb. 27, 2020	Feb. 20, 2020	Feb. 21, 2019	Feb. 20, 2019	Apr. 30, 2018	Feb. 15, 2018	Mar. 16, 2017	Aug. 11, 2016	Jun. 15, 2016	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jun. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares, issued													24,298,651		24,298,651		25,245,740	24,298,651
Common stock, shares, outstanding													24,298,651		24,298,651		25,245,740	24,298,651
Common stock, par value												$ 0.01	$ 0.01		$ 0.01		$ 0.01	$ 0.01
Share repurchase program, authorized amount		$ 100,000,000.0						$ 40,000,000.0				$ 30,000,000.0
Stock repurchase program, expiration date		Mar. 12, 2023						Jun. 15, 2020				Jun. 15, 2018
Stock repurchase program period in force								2 years				2 years
Share repurchase program, treasury stock shares															1,644,697			2,382,155
Share repurchase program, treasury stock, value													$ 13,531,000		$ 44,530,000			$ 61,224,000
Share repurchase program, treasury stock, per share																		$ 25.70
Common stock, shares, retired													1,418,898		1,644,697
Treasury stock, shares													0		0			0
Aggregate sale price of common stock													$ (55,000)	$ 9,452,000	$ 27,125,000	$ 9,452,000
Shares issued average price per share							$ 48.52
Proceeds from issuance of common stock							$ 28,000,000,000								$ 27,125,000	$ 9,452,000
Common Stock
Class Of Stock [Line Items]
Common stock, shares, issued													24,298,651	23,895,442	24,298,651	23,895,442	25,245,740	24,298,651	25,717,549	23,643,277	23,499,635
Common stock, shares, retired													1,418,898		1,644,697
Aggregate sale price of common stock														$ 3,000	$ 6,000	$ 3,000
Restricted Stock Units
Class Of Stock [Line Items]
Restricted stock units, granted															285,035
At-the-Market Offering
Class Of Stock [Line Items]
Shares, issued															560,000
2019 At-the-Market Offering
Class Of Stock [Line Items]
Shares, issued															560,000		1,565,322
Shares issued average price per share															$ 50.00		$ 45.98
Proceeds from issuance of common stock															$ 28,000,000.0		$ 72,000,000.0
Stock issuance costs															400,000		1,100,000
Other stock issuance costs															$ 400,000		$ 1,000,000.0
2019 At-the-Market Offering | Common Stock
Class Of Stock [Line Items]
Common stock, par value							$ 0.01
2019 At-the-Market Offering | Maximum | Common Stock
Class Of Stock [Line Items]
Aggregate sale price of common stock				$ 100,000,000			$ 100,000,000
2020 At-the-Market Offering
Class Of Stock [Line Items]
Common stock, par value			$ 0.01
2020 At-the-Market Offering | Common Stock
Class Of Stock [Line Items]
Shares, issued													0		0
2020 At-the-Market Offering | Maximum | Common Stock
Class Of Stock [Line Items]
Aggregate sale price of common stock			$ 225,000,000
2016 LTIP
Class Of Stock [Line Items]
Common stock, shares, issued															137,608
Common stock, shares, issued													559,159		559,159			559,159
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													$ 1,300,000	$ 1,400,000	$ 2,600,000	$ 2,700,000
Dividends earned on restricted stock units													$ 700,000		$ 700,000			$ 700,000
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	116,852				168,183	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