Related Party Transactions (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended								9 Months Ended	12 Months Ended
	May 31, 2019	Sep. 30, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transactions
Net proceeds from issuance of common stock												$ 52,714	$ 64,880	$ 0
Management fees			$ 1,987	$ 1,800	$ 1,832	$ 1,735	$ 1,950	$ 2,284	$ 2,259	$ 2,180		$ 7,354	8,673	8,100
Western Asset Management Company
Related Party Transactions
Management fees (as a percent)												1.50%
Renewal term of management agreement												1 year
Notice period to terminate the Management Agreement following initial term												180 days
Prior period over which management fees were incurred used to calculate the termination fee under the Management Agreement												24 months
Notice period to terminate the Management Agreement for cause												30 days
Management fees												$ 7,400	8,700	8,100
Reimbursable employee costs												1,600	1,500	$ 1,400
Management fees incurred but not yet paid			2,000				4,200					2,000	4,200
Accounts payable, related parties			$ 181				$ 379					$ 181	$ 379
Western Asset Management Company | Minimum
Related Party Transactions
Proportion of affirmative votes by the entity's independent directors to terminate the Management Agreement (as a percent)												67.00%
Proportion of votes required by the entity's independent directors for acceptance of reduction in management fees (as a percent)												67.00%
Secondary Offering
Related Party Transactions
Sale of stock, number of shares issued in transaction (in shares)	5,000,000	6,500,000									6,500,000
Net proceeds from issuance of common stock	$ 49,300	$ 67,700