Use of Derivative Financial Instruments - Risk Management and Unsecured Loan Swaps (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Interest Rate Swaps
Unsecured Term Loan Swaps
Notional amount	$ 450,000
Interest Rate Derivative, PNC Bank, October 10, 2012
Unsecured Term Loan Swaps
Notional amount	10,000
Fair value	$ 8
Fixed Interest Rate (as a percent)	0.7945%
Interest Rate Derivative, Bank of America, October 10, 2012
Unsecured Term Loan Swaps
Notional amount	$ 10,000
Fair value	$ 8
Fixed Interest Rate (as a percent)	0.7945%
Interest Rate Derivative, UBS AG, October 10, 2012
Unsecured Term Loan Swaps
Notional amount	$ 10,000
Fair value	$ 8
Fixed Interest Rate (as a percent)	0.7945%
Interest Rate Derivative, Royal Bank of Canada, October 10, 2012
Unsecured Term Loan Swaps
Notional amount	$ 10,000
Fair value	$ 8
Fixed Interest Rate (as a percent)	0.7945%
Interest Rate Derivative, RJ Capital Services, Inc, October 10, 2012, One
Unsecured Term Loan Swaps
Notional amount	$ 10,000
Fair value	$ 8
Fixed Interest Rate (as a percent)	0.7975%
Interest Rate Derivative, Bank of America, October 10, 2012, Two
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 23
Fixed Interest Rate (as a percent)	0.7525%
Interest Rate Derivative, RJ Capital Services, October 10, 2012, Two
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 24
Fixed Interest Rate (as a percent)	0.727%
Interest Rate Derivative, Regions Bank, March 01, 2013
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 177
Fixed Interest Rate (as a percent)	1.33%
Interest Rate Derivative, Capital One, June 01, 2013
Unsecured Term Loan Swaps
Notional amount	$ 50,000
Fair value	$ (102)
Fixed Interest Rate (as a percent)	1.681%
Interest Rate Derivative, Capital One, August 01, 2013
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ (65)
Fixed Interest Rate (as a percent)	1.703%
Interest Rate Derivative, Regions Bank, February 03, 2014
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ (254)
Fixed Interest Rate (as a percent)	1.9925%
Interest Rate Derivative, The Toronto-Dominion Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 238
Fixed Interest Rate (as a percent)	1.383%
Interest Rate Derivative, PNC Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount	$ 50,000
Fair value	$ 466
Fixed Interest Rate (as a percent)	1.3906%
Interest Rate Derivative, Regions Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount	$ 35,000
Fair value	$ 329
Fixed Interest Rate (as a percent)	1.3858%
Interest Rate Derivative, US Bank, September 29, 2016
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 230
Fixed Interest Rate (as a percent)	1.395%
Interest Rate Derivative, Capital One, September 29, 2016
Unsecured Term Loan Swaps
Notional amount	$ 15,000
Fair value	$ 137
Fixed Interest Rate (as a percent)	1.395%
Interest Rate Derivative, Royal Bank of Canada, March 20, 2015
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 19
Fixed Interest Rate (as a percent)	1.709%
Interest Rate Derivative, The Toronto-Dominion Bank, March 20, 2015
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 17
Fixed Interest Rate (as a percent)	1.7105%
Interest Rate Derivative, The Toronto-Dominion Bank, September 10, 2017
Unsecured Term Loan Swaps
Notional amount	$ 100,000
Fair value	$ (1,605)
Fixed Interest Rate (as a percent)	2.2255%
Interest Rate Derivative, Wells Fargo Bank, March 20, 2015
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ 1
Fixed Interest Rate (as a percent)	1.828%
Interest Rate Derivative, The Toronto-Dominion Bank, February 14, 2020
Unsecured Term Loan Swaps
Notional amount	$ 25,000
Fair value	$ (166)
Fixed Interest Rate (as a percent)	2.4535%
Interest Rate Derivative, Regions Bank, February 14, 2020
Unsecured Term Loan Swaps
Notional amount	$ 50,000
Fair value	$ (355)
Fixed Interest Rate (as a percent)	2.475%
Interest Rate Derivative, Capital One, February 14, 2020
Unsecured Term Loan Swaps
Notional amount	$ 50,000
Fair value	$ (408)
Fixed Interest Rate (as a percent)	2.53%