Derivative Instruments (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Interest Rate Derivatives [Abstract]
Number of interest rate swap contracts	3
aggregate notional amount	$ 103,200,000		$ 103,600,000
Termination value of interest rate swap, including accrued interest	9,100,000
Interest Rate Cash Flow Hedges [Abstract]
Change in fair value of swaps as a decrease to other comprehensive income	1,299,000	871,000
Amount of loss reclassified into interest expense from AOCI	352,000	360,000
Ineffective portion of the change in the fair value of swaps as an adjustment to interest expense	59,000	18,000
Fair value of interest rate swaps	9,000,000		8,500,000
Amount estimated to be reclassified from accumulated other comprehensive income as an adjustment to interest expense	$ 1,200,000