Derivative Instruments and Hedging Activities - Interest Rate Swaps (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Amount of (gain)/loss recognized in OCI on derivative (effective portion)	$ (869)	$ 813	$ 1,900
Escrow Deposits, Goodwill and other Assets
Derivative [Line Items]
Interest Rate Swap	942
Accrued expenses and accounts payable
Derivative [Line Items]
Interest Rate Swap		227
Cash Flow Hedging | Interest Expense | Interest Rate Swap
Derivative [Line Items]
Amount of loss reclassified from accumulated OCI into income (effective portion)	$ 300	$ 1,139	$ 1,728