Derivative Instruments and Hedging Activities - Effect of Interest Rate Swaps on Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
5 year interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate swaps reclassified to earnings	$ (23)	$ 31	$ (27)	$ 136
10 year interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate swaps reclassified to earnings	27	81	120	283
Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate swaps reclassified to earnings	$ 4	$ 112	$ 93	$ 419