Derivative Financial Instruments (Schedule of the changes in the fair value of non-hedge accounting derivatives) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Total impact on other non-interest income	$ 114	$ 9,793	$ 5,066
Operating Expense [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Total impact on other non-interest income	2,702	8,668	4,361
Operating Expense [Member] | Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member]
Derivative [Line Items]
Total impact on other non-interest income	242	(361)	(33)
Operating Expense [Member] | Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member]
Derivative [Line Items]
Total impact on other non-interest income	(2,062)	1,553	801
Operating Expense [Member] | Not Designated as Hedging Instrument [Member] | Other Contract [Member]
Derivative [Line Items]
Total impact on other non-interest income	$ (768)	$ (67)	$ (63)