Derivative Instruments and Hedging Activities - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Fair Value (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	$ 171	$ (263)	$ (218)	$ (155)
Designated as Fair Value Hedge | Interest Income | Interest Rate Swaps
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	129	(93)	32	10
Designated as Fair Value Hedge | Interest Income | Loans and Long-term Borrowings | Derivatives designated as hedging instruments:
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	(129)	93	(32)	(10)
Designated as Fair Value Hedge | Interest Expense | Interest Rate Swaps
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	(127)	4,302	6,670	3,211
Designated as Fair Value Hedge | Interest Expense | Loans and Long-term Borrowings | Derivatives designated as hedging instruments:
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	$ 133	$ (4,329)	$ (6,646)	$ (3,270)