Derivative Instruments (Narrative) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Notional Amount of Derivatives	$ 797,474,000	$ 740,332,000
Real Estate And Building Materials [Member]
Derivative [Line Items]
Derivative loss from industry concentration	2,700,000
Education [Member]
Derivative [Line Items]
Derivative loss from industry concentration	2,600,000
Manufacturing [Member]
Derivative [Line Items]
Derivative loss from industry concentration	1,300,000
Fair Value Hedging [Member]
Derivative [Line Items]
Notional Amount of Derivatives	6,300,000
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Derivatives	$ 651,100,000