Investment Securities (Narrative) (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) position security	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) position security	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) position security
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 1,013,539,000		$ 1,013,539,000		$ 964,534,000
Investment securities held to maturity	$ 478,846,000		$ 478,846,000		$ 473,684,000
Total number of all held to maturity and available for sale securities in an unrealized loss position | security	28		28		163
Amortized cost	$ 990,205,000		$ 990,205,000		$ 957,938,000
Proceeds from maturities, prepayments and calls of short-term investments		$ 14,000,000		$ 14,000,000
Gross gains		643,000	95,000	643,000
Gross losses		0	$ 0	0
Proceeds from calls on securities available for sale				465,000
Recognized gain on calls of securities				2,000
Number of securities in an unrealized loss position | position	7		7		64
Other-than-temporary impairment charges, net	$ 0		$ 0
Proceeds from calls of held to maturity securities	4,300,000	$ 9,100,000	14,900,000	13,200,000
Recognized gain on calls of securities, held-to-maturity portfolio	1,000		2,000
Recognized loss on calls of securities held-to-maturity portfolio	$ 0		$ 0
Number of securities in an unrealized loss position | position	21		21		99
Available-for-sale Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Gross losses				$ 0
Proceeds from the sale of securities available for sale			$ 2,200,000
Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 1,800,000		$ 1,800,000
Number of securities in an unrealized loss position | position	3		3
Unrealized losses			$ 26,000
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	$ 1,200,000		1,200,000
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	923,853,000		923,853,000		$ 863,861,000
Investment securities held to maturity	1,192,000		1,192,000		1,597,000
Amortized cost	901,392,000		901,392,000		857,430,000
Equity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	531,000		531,000		519,000
Amortized cost	$ 397,000		$ 397,000		$ 397,000
External Credit Rating, Non Investment Grade [Member] | Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Number of securities in an unrealized loss position | position	1		1