Derivative Financial Instruments (Effect of Derivative Instruments on Comprehensive Income) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivatives Not Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 4,064		$ 4,870
Interest Rate Contract [Member] | Derivatives In Cash Flow Hedging Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Recognized in OCI	(1,659)	(10,511)	(4,139)	(15,286)
Interest Rate Contract [Member] | Other Income [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(4,054)	(362)	(4,823)	152
Interest Rate Contract [Member] | Other Expense [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	(10)	(36)	(47)	(159)
Interest Rate Contract [Member] | Other Expense [Member] | Derivatives In Cash Flow Hedging Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss)Recognized in Income (Ineffective Portion)	0	291	0	509
Interest Rate Contract [Member] | Interest Expense [Member] | Derivatives In Cash Flow Hedging Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Reclassified from Accumulated OCI into Income	$ (4,434)	$ (4,687)	$ (13,083)	$ (12,312)