Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) (Fixed rate long-term borrowings [Member], Fair Value Hedges [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fixed rate long-term borrowings [Member] | Fair Value Hedges [Member]
Derivative [Line Items]
Notional amount	$ 1,400,000	$ 900,000
Average maturity (in years)	3 years 10 months 24 days	4 years 4 months 24 days
Weighted-average rate, Fixed	4.42%	6.07%
Weighted-average rate, Variable	1.22%	1.85%