Derivatives and Hedging Activities (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) Financial_Instrument	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Expected amount of derivative related interest to be reclassified to interest expense over the next 12 months	$ 1,023,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Derivative asset	1,065,000	$ 44,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Accounts Payable And Other Liabilities [Member]
Derivative [Line Items]
Derivative liabilities	$ 0	(1,077,000)
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Number of derivative instruments held | Financial_Instrument	10
Notional amount of derivatives	$ 505,000,000
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Interest Expense [Member]
Derivative [Line Items]
Amount of loss recognized in OCI on derivatives (effective portion)	1,168,000	(3,084,000)
Amount of loss reclassified from Accumulated OCI into income (effective portion)	$ 930,000	$ 3,990,000