Derivative Financial Instruments (Narrative) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
Derivative [Line Items]
Fair value of derivatives in net liability position with credit-risk-related Contingent Features	$ 57,946	$ 57,946
Cash collateral posted with derivative counterparties	75,490	75,490
Derivatives In Cash Flow Hedging Relationships [Member]
Derivative [Line Items]
Aggregate notional amount designated as cash flow hedges	1,156,473	1,156,473
Derivatives In Cash Flow Hedging Relationships [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Number of derivative instruments held	14	14
Derivatives In Cash Flow Hedging Relationships [Member] | Interest Expense [Member]
Derivative [Line Items]
Estimated amount to be reclassified	18,600
Future annual time period	12 months
Derivatives Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Number of derivative instruments held	168	168
Aggregate notional amount derivative	890,124	890,124
Net loss related to changes in fair value of derivatives	$ 4,064	$ 4,870