Derivative Financial Instruments - Risk Management and Unsecured Loan Swaps (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Interest Rate Swaps
Unsecured Term Loan Swaps
Notional amount assets	$ 0	$ 250,000
Notional amount liabilities	1,275,000	850,000
Notional amount liabilities	1,275,000	$ 850,000
Interest Rate Derivative, The Toronto-Dominion Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount liabilities	25,000
Derivative Liability, Fair Value, Gross Liability	$ (76)
Fixed Interest Rate (as a percent)	1.383%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (76)
Fixed Interest Rate (as a percent)	1.383%
Interest Rate Derivative, PNC Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (153)
Fixed Interest Rate (as a percent)	1.3906%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (153)
Fixed Interest Rate (as a percent)	1.3906%
Interest Rate Derivative, Regions Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount liabilities	$ 35,000
Derivative Liability, Fair Value, Gross Liability	$ (106)
Fixed Interest Rate (as a percent)	1.3858%
Notional amount liabilities	$ 35,000
Derivative Liability, Fair Value, Gross Liability	$ (106)
Fixed Interest Rate (as a percent)	1.3858%
Interest Rate Derivative, US Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (77)
Fixed Interest Rate (as a percent)	1.395%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (77)
Fixed Interest Rate (as a percent)	1.395%
Interest Rate Derivative, Capital One, September 29, 2016
Unsecured Term Loan Swaps
Notional amount liabilities	$ 15,000
Derivative Liability, Fair Value, Gross Liability	$ (46)
Fixed Interest Rate (as a percent)	1.395%
Notional amount liabilities	$ 15,000
Derivative Liability, Fair Value, Gross Liability	$ (46)
Fixed Interest Rate (as a percent)	1.395%
Interest Rate Derivative, Royal Bank of Canada, March 20, 2015
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (280)
Fixed Interest Rate (as a percent)	1.709%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (280)
Fixed Interest Rate (as a percent)	1.709%
Interest Rate Derivative, The Toronto-Dominion Bank, March 20, 2015
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (280)
Fixed Interest Rate (as a percent)	1.7105%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (280)
Fixed Interest Rate (as a percent)	1.7105%
Interest Rate Derivative, The Toronto-Dominion Bank, September 10, 2017
Unsecured Term Loan Swaps
Notional amount liabilities	$ 100,000
Derivative Liability, Fair Value, Gross Liability	$ (1,493)
Fixed Interest Rate (as a percent)	2.2255%
Notional amount liabilities	$ 100,000
Derivative Liability, Fair Value, Gross Liability	$ (1,493)
Fixed Interest Rate (as a percent)	2.2255%
Interest Rate Derivative, Wells Fargo Bank, March 20, 2015
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (750)
Fixed Interest Rate (as a percent)	1.828%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (750)
Fixed Interest Rate (as a percent)	1.828%
Interest Rate Derivative, The Toronto-Dominion Bank, February 14, 2020
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,027)
Fixed Interest Rate (as a percent)	2.4535%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,027)
Fixed Interest Rate (as a percent)	2.4535%
Interest Rate Derivative, Regions Bank, February 14, 2020
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (2,072)
Fixed Interest Rate (as a percent)	2.475%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (2,072)
Fixed Interest Rate (as a percent)	2.475%
Interest Rate Derivative, Capital One, February 14, 2020
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (2,121)
Fixed Interest Rate (as a percent)	2.53%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (2,121)
Fixed Interest Rate (as a percent)	2.53%
Interest Rate Derivative, The Toronto-Dominion Bank, October 30, 2017
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,093)
Fixed Interest Rate (as a percent)	1.8485%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,093)
Fixed Interest Rate (as a percent)	1.8485%
Interest Rate Derivative, Royal Bank of Canada, October 30, 2017
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,094)
Fixed Interest Rate (as a percent)	1.8505%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,094)
Fixed Interest Rate (as a percent)	1.8505%
Interest Rate Derivative, Wells Fargo Bank, October 30, 2017
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,094)
Fixed Interest Rate (as a percent)	1.8505%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,094)
Fixed Interest Rate (as a percent)	1.8505%
Interest Rate Derivative, PNC Bank, $25m, October 30, 2017
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,093)
Fixed Interest Rate (as a percent)	1.8485%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (1,093)
Fixed Interest Rate (as a percent)	1.8485%
Interest Rate Derivative, PNC Bank, $50m, October 30, 2017
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (2,184)
Fixed Interest Rate (as a percent)	1.8475%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (2,184)
Fixed Interest Rate (as a percent)	1.8475%
Interest Rate Derivative, TD Bank, $75m, Sep 29, 2020
Unsecured Term Loan Swaps
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (290)
Fixed Interest Rate (as a percent)	0.275%
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (290)
Fixed Interest Rate (as a percent)	0.275%
Interest Rate Derivative, Wells Fargo Bank, $75m, Sep 29, 2020
Unsecured Term Loan Swaps
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (298)
Fixed Interest Rate (as a percent)	0.279%
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (298)
Fixed Interest Rate (as a percent)	0.279%
Interest Rate Derivative, TD Bank, $75m, March 19, 2021
Unsecured Term Loan Swaps
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (251)
Fixed Interest Rate (as a percent)	0.275%
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (251)
Fixed Interest Rate (as a percent)	0.275%
Interest Rate Derivative, Wells Fargo Bank, $75m, March 19, 2021
Unsecured Term Loan Swaps
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (258)
Fixed Interest Rate (as a percent)	0.28%
Notional amount liabilities	$ 75,000
Derivative Liability, Fair Value, Gross Liability	$ (258)
Fixed Interest Rate (as a percent)	0.28%
Interest Rate Derivative, The Toronto-Dominion Bank, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,932)
Fixed Interest Rate (as a percent)	2.918%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,932)
Fixed Interest Rate (as a percent)	2.918%
Interest Rate Derivative, PNC Bank, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,932)
Fixed Interest Rate (as a percent)	2.919%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,932)
Fixed Interest Rate (as a percent)	2.919%
Interest Rate Derivative, Bank of Montreal, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,932)
Fixed Interest Rate (as a percent)	2.919%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,932)
Fixed Interest Rate (as a percent)	2.919%
Interest Rate Derivative, US Bank, July 26, 2019 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (2,466)
Fixed Interest Rate (as a percent)	2.919%
Notional amount liabilities	$ 25,000
Derivative Liability, Fair Value, Gross Liability	$ (2,466)
Fixed Interest Rate (as a percent)	2.919%
Interest Rate Derivative, Wells Fargo Bank, July 15, 2020 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,633)
Fixed Interest Rate (as a percent)	2.246%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,633)
Fixed Interest Rate (as a percent)	2.246%
Interest Rate Derivative, US Bank, July 15, 2020 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,632)
Fixed Interest Rate (as a percent)	2.2459%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,632)
Fixed Interest Rate (as a percent)	2.2459%
Interest Rate Derivative, Regions Bank, July 15, 2020 [Member]
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,632)
Fixed Interest Rate (as a percent)	2.2459%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (4,632)
Fixed Interest Rate (as a percent)	2.2459%
Interest Rate Derivative, Bank of Montreal, July 15, 2020
Unsecured Term Loan Swaps
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (3,436)
Fixed Interest Rate (as a percent)	1.7165%
Notional amount liabilities	$ 50,000
Derivative Liability, Fair Value, Gross Liability	$ (3,436)
Fixed Interest Rate (as a percent)	1.7165%