Commitments, Contingencies and Derivatives (Commercial Loan Swaps) (Detail) - Interest Rate Swap [Member] swap in Thousands, $ in Thousands	Dec. 31, 2017 USD ($) swap	Dec. 31, 2016 USD ($) swap	Dec. 31, 2015 USD ($)
Derivative Asset [Abstract]
Derivative, Fair Value, Net		$ (7,571)	$ (8,372)
Notional Amount	$ 43,000	$ 43,000
federal home loan bank 30-day [Member]
Derivative Liability [Abstract]
Derivative Liability, Number of Instruments Held | swap	42	50
Derivative Liability, Notional Amount	$ 226,884	$ 266,263
Derivative, Net Liability Position, Aggregate Fair Value	$ (5,036)	$ (1,945)
Derivative Asset [Abstract]
Derivative Asset, Number of Instruments Held | swap	23	0
Derivative Asset, Notional Amount	$ 124,784	$ 0
Derivative, Fair Value, Net	$ 1,799	$ 0
Commercial and Industrial Sector [Member]
Derivative Asset [Abstract]
Derivative Asset, Number of Instruments Held | swap	65	50
Derivative Asset, Notional Amount	$ 351,668	$ 266,263
Derivative, Fair Value, Net	3,237	1,945
Loans [Member]
Derivative Asset [Abstract]
Derivative, Fair Value, Net	$ 0	$ 0
Derivative, Number of Instruments Held | swap	130	100
Notional Amount	$ 703,336	$ 532,526