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Debt - Unsecured Term Loans (Details) - USD ($)	Dec. 31, 2018	Dec. 21, 2018	Dec. 03, 2018	Nov. 05, 2015
Wells Fargo, Merrill Lynch, Pierce Fenner Smith, PNC Capital Markets Credit Facility
Debt Instrument [Line Items]
Issuance costs, net of accumulated amortization				$ (1,179,000)
$250.0 million 5 year - variable rate \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount	$ 250,000,000
Unsecured term loans	$ 50,000,000
Stated interest rate (percent)	3.5493%
$250.0 million 5 year - variable rate \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount	$ 250,000,000
Unsecured term loans	$ 26,000,000
Stated interest rate (percent)	3.6794%
$150.0 million 5.5 year - variable rate \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount	$ 150,000,000
Unsecured term loans	$ 100,000,000
Stated interest rate (percent)	3.5493%
$150.0 million 5.5 year - variable rate \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount	$ 150,000,000
Unsecured term loans	$ 26,000,000
Stated interest rate (percent)	3.6794%
Term Loan \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount		$ 400,000,000
Unsecured term loans	$ 352,000,000
Issuance costs, net of accumulated amortization	(3,145,000)	$ (1,966,000)
Term Loan \| Line of Credit
Debt Instrument [Line Items]
Total debt, net	348,855,000
Interest Rate Swap One \| $250.0 million 5 year - swapped to fixed rate \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount	250,000,000
Unsecured term loans	$ 90,000,000
Stated interest rate (percent)	2.551%
Interest Rate Swap One \| $250.0 million 5 year - variable rate \| Unsecured Debt \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, derivative			1.20%
Interest Rate Swap One \| $250.0 million 5 year - variable rate \| Unsecured Debt \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, derivative		1.20%
Interest Rate Swap One \| Term Loan \| Unsecured Debt \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, derivative	1.20%
Interest Rate Swap Two \| $250.0 million 5 year - swapped to fixed rate \| Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount	$ 250,000,000
Unsecured term loans	$ 60,000,000
Stated interest rate (percent)	2.5525%
Interest Rate Swap Two \| Term Loan \| Unsecured Debt \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate, derivative	1.20%