Derivatives (Effect of Derivative Instruments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Included in Interest Income / (Expense)	$ 19,031	$ 18,791	$ 18,321	$ 18,196	$ 18,388	$ 17,192	$ 16,712	$ 16,225	$ 74,339	$ 68,517	$ 66,248
Interest Rate Swaps
Derivative [Line Items]
Included in Interest Income / (Expense)									0	0	0
Included in Other Income / (Expense)									$ 15	$ 528	$ 163