Investment Securities (Narrative) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 security position	Mar. 31, 2014	Dec. 31, 2014 position security
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 1,047,559,000		$ 1,074,395,000
Investment securities held to maturity	473,704,000		469,528,000
Total number of all held to maturity and available for sale securities in an unrealized loss position	131		206
Other-than-temporary impairment charges, net	0
Amortized cost	1,028,428,000		1,061,461,000
Proceeds from the sale of securities available for sale	0	6,085,000
Gross gains		365,000
Recognized gain on calls of securities	2,000
Gross losses		0
Proceeds from calls on securities available for sale	465,000	740,000
Gross gains	2,000
Loss on the sale of a previously impaired non-agency mortgage-backed security		365,000
Previously incurred cumulative credit losses		1,500,000
Number of securities in an unrealized loss position	21		43
Proceeds from calls on securities available for sale		4,073,000
Recognized gain on calls of securities held to maturity portfolio		13,000
Proceeds from the calls		6,395,000
Proceeds from sale of securities held to maturity portfolio	0	0
Fair value	487,671,000		482,473,000
Number of securities in an unrealized loss position	110		163
Available-for-sale Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Gross losses	0	0
Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	3,003,000
Number of securities in an unrealized loss position	4
Unrealized losses	21,000
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Investment securities held to maturity	2,500
Fair value	$ 2,600