Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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Fair value as of the balance sheet date of all interest rate derivatives designated as cash flow hedging instruments.

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Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

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Derivative Instruments (Details)	3 Months Ended
Derivative Instruments (Details)	Mar. 31, 2019 USD ($) contract	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Maximum period of extension term	72 months
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net [Abstract]
Gross derivative assets	$ 554,000		$ 1,199,000
Gross derivative liabilities	(2,443,000)		(839,000)
Net derivative asset/(liability)	(1,889,000)		$ 360,000
Amount of gain/(loss) recognized in OCI	(2,024,000)	$ 1,517,000
Total amount of Interest Expense presented in the consolidated statements of income	(15,493,000)	(13,758,000)
Total amount of Loss on Extinguishment of Debt presented in the consolidated statements of income	0	(1,680,000)
Loss on write off of discount and unamortized debt issuance costs	400,000
Gain (loss) to be reclassified	2,200,000
Gain (loss) from hedge ineffectiveness	0	0
Interest rate swaps
Derivative [Line Items]
Total Notional Amount (in millions)	450,000,000
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net [Abstract]
Total amount of Interest Expense presented in the consolidated statements of income	(15,493,000)	(13,758,000)
Interest rate swaps \| Interest Expense
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net [Abstract]
Amount of gain/(loss) recognized in OCI	(2,024,000)	1,517,000
Amount of gain/(loss) reclassified from OCI	771,000	206,000
Interest rate swaps \| Gain (Loss) On Extinguishment Of Debt
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net [Abstract]
Amount of gain/(loss) reclassified from OCI	0	$ (1,258,000)
Credit Risk Contract
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net [Abstract]
Assets needed for immediate settlement, aggregate fair value	2,100,000
Unsecured Debt \| Amended and Restated $300 Million Unsecured 2011 Term Loan
Derivative [Line Items]
Face amount of debt instrument	$ 300,000,000
Unsecured Debt \| Amended and Restated $300 Million Unsecured 2011 Term Loan \| Interest rate swaps
Derivative [Line Items]
Number of Swap Agreements \| contract	3
Total Notional Amount (in millions)	$ 300,000,000
Unsecured Debt \| $250 Million Unsecured 2018 Term Loan
Derivative [Line Items]
Face amount of debt instrument	250,000,000
Hedged portion of long-term debt	150,000,000
Total Notional Amount (in millions)	$ 150,000,000
Unsecured Debt \| $250 Million Unsecured 2018 Term Loan \| Interest rate swaps
Derivative [Line Items]
Number of Swap Agreements \| contract	2
Total Notional Amount (in millions)	$ 100,000,000
Unsecured Debt \| $250 Million Unsecured 2018 Term Loan Maturing 2020 \| Interest rate swaps
Derivative [Line Items]
Number of Swap Agreements \| contract	1
Total Notional Amount (in millions)	$ 50,000,000