Derivative Instruments and Hedging Activities - Gains (Losses) on Interest Rate Derivatives Designated as Fair Value Hedges (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income and interest expense	$ 37	$ 171	$ (753)	$ (218)
Designated as fair value hedge | Interest income | Interest rate swaps
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income and interest expense	75	129	224	32
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]
Interest income and interest expense	(75)	(129)	(224)	(32)
Designated as fair value hedge | Interest expense | Interest rate swaps
Gain Loss On Fair Value Hedges Recognized In Earnings [Line Items]
Interest income and interest expense	0	(127)	0	6,670
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]
Interest income and interest expense	$ 0	$ 133	$ 0	$ (6,646)