Derivative Instruments and Hedging Activities - Gains (Losses) on Interest Rate Derivatives Designated as Fair Value Hedges (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	$ 70	$ (92)	$ (790)	$ (389)
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	52	2	149	(97)
Designated as Fair Value Hedge | Interest income | Loans and borrowings | Derivatives designated as hedging instruments:
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	(52)	(2)	(149)	97
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	0	2,069	0	6,797
Designated as Fair Value Hedge | Interest expense | Loans and borrowings | Derivatives designated as hedging instruments:
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Gains (losses) on derivatives	$ 0	$ (2,060)	$ 0	$ (6,779)