Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities - Interest Rate Swaps (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Amount of loss recognized in OCI on derivative (effective portion)	$ 1,900	$ 1,230	$ 188
Deferred commission expense	(5,871)	(6,272)	(5,011)
Accrued expenses and accounts payable
Derivative [Line Items]
Interest Rate Swap	553	381
Cash Flow Hedging | Interest Expense | Interest Rate Swap
Derivative [Line Items]
Amount of loss reclassified from accumulated OCI into income (effective portion)	$ 1,728	$ 1,776	$ 1,851