Derivatives (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Fair value of collateral pledged to secure interest rate contracts	$ 7,005
Incremental interest expense paid to interest rate swap counterparties	3,321	3,281	3,095
Interest Rate Swap
Derivative [Line Items]
Gain (loss) expected to be reclassified in next 12 months	(2,193)
2011 Interest Rate Swap
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 93,500
Fixed rate payments, interest rate	5.50%	5.50%	5.50%
Variable rate payment rate	1.75%	1.75%	1.75%