Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities - Interest Rate Derivatives Designated as Hedges (Details) - Derivatives designated as hedging instruments - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Total net carrying amount	$ 614,717	$ 614,775
Fair value hedge | Interest rate swaps
Derivative [Line Items]
Loan receivable - carrying amount	8,224
Cumulative fair value adjustment	(507)
Total net carrying amount	$ 7,717	$ 7,775