Derivative Financial Instruments - Schedule fair value of derivative instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Other Assets	$ 44,333	$ 48,391
Other Liabilities	26,102	32,180
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Other Assets	3,907	4,481
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative [Line Items]
Other Liabilities	1,219	4,598
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Other Assets	44,174	48,209
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative [Line Items]
Other Liabilities	25,878	31,915
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Other Assets	159	182
Credit Risk Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative [Line Items]
Other Liabilities	218	258
Other Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Assets [Member]
Derivative [Line Items]
Other Assets	0	0
Other Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Derivative [Line Items]
Other Liabilities	$ 6	$ 7