Investment Securities (Narrative) (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($) position security	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) position security
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 984,206,000		$ 964,534,000
Investment securities held to maturity	$ 472,934,000		$ 473,684,000
Total number of all held to maturity and available for sale securities in an unrealized loss position | security	53		163
Amortized cost	$ 965,852,000		$ 957,938,000
Gross gains	95,000
Gross losses	0
Proceeds from maturities, prepayments and calls of short-term investments	0
Proceeds from maturities, calls and paydowns of securities available for sale	$ 40,818,000	$ 45,848,000
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	15		64
Other-than-temporary impairment charges, net	$ 0
Recognized gain (loss) on calls of securities held to maturity portfolio	1,000	0
Proceeds from calls of held to maturity securities	516,000	4,100,000
Proceeds from maturities, calls and paydowns of investment securities held to maturity	11,805,000	5,343,000
Investment securities held to maturity, fair value	$ 491,349,000		$ 488,331,000
Number of securities in an unrealized loss position | position	38		99
Available-for-sale Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Proceeds from the sale of securities available for sale	$ 2,106,000
Gross losses		$ 0
Proceeds from maturities, calls and paydowns of securities available for sale	0
Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 690,000
Number of securities in an unrealized loss position | position	3
Unrealized losses	$ 5,000
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	1,400,000
Investment securities held to maturity, fair value	1,500,000
Equity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	521,000		$ 519,000
Amortized cost	397,000		397,000
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	886,641,000		863,861,000
Investment securities held to maturity	1,403,000		1,597,000
Amortized cost	868,946,000		857,430,000
Investment securities held to maturity, fair value	$ 1,458,000		$ 1,658,000