Derivative Financial Instruments (Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives) (Detail) (Not Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Rate Contract [Member] \| Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	$ 1,786	$ 1,441	$ 4,722
Interest Rate Contract [Member] \| Other Non-Interest Expense [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	(2)	(96)	(116)
Commodity Contract [Member] \| Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	118	496	124
Foreign Exchange Contract [Member] \| Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	$ 162	$ 175	$ 0

Derivative Financial Instruments (Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives) (Detail) (Not Designated as Hedging Instrument [Member], USD $)
In Thousands, unless otherwise specified

12 Months Ended

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Interest Rate Contract [Member] | Other Non-Interest Income [Member]

Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]

Amount of gain (loss) included in income (expense)

$ 1,786

$ 1,441

$ 4,722

Interest Rate Contract [Member] | Other Non-Interest Expense [Member]

Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]