Derivatives and Hedging Activities (Narrative) (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 28, 2014	Jan. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative [Line Items]
Gain (loss) on derivative instruments, net			$ 311,000	$ 14,207,000	$ (717,000)	$ 7,086,000
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Assets needed for immediate settlement, aggregate fair value			11,100,000		11,100,000
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Assets needed for immediate settlement, aggregate fair value			11,100,000		11,100,000
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative gain (loss) to be reclassified during next 12 months			8,500,000		8,500,000
Treasury Lock [Member]
Derivative [Line Items]
Derivative, notional amount		$ 250,000,000
Term of derivative contract		10 years
Loss from settlement of derivative	$ 3,900,000
Treasury Lock [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative loss recognized in current year			100,000		300,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, notional amount			1,248,630,000		1,248,630,000
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, notional amount			51,400,000		51,400,000
Amount of gain (loss) recognized in income on derivative (ineffective portion, reclassifications of missed forecasted transactions and amounts excluded from effectiveness testing)			$ 300,000		$ (700,000)
Gain (loss) on derivative instruments, net				$ 14,200,000		$ 7,100,000