Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014 security position	Jun. 30, 2013	Jun. 30, 2014 security position	Jun. 30, 2013	Dec. 31, 2013 security position
Schedule of Held-to-maturity Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	$ 59,000		$ 365,000
Proceeds from maturities, calls and paydowns of securities available for sale			91,710,000	196,434,000
Available for sale investment securities	1,156,986,000		1,156,986,000		1,157,594,000
Investment securities held to maturity	454,648,000		454,648,000		357,500,000
Total number of all held to maturity and available for sale securities in an unrealized loss position	408		408		346
Proceeds from the sale of securities available for sale		6,915,000	14,483,000	14,310,000
Gross gains	150,000	407,000	150,000	888,000
Gross losses		0	404,000	0
Proceeds from calls on securities available for sale		896,000	740,000	896,000
Recognized gain on calls of securities			2,000
Other-than-temporary impairment charges, net			0
Number of securities in an unrealized loss position	75		75		76
Amortized cost	1,145,778,000		1,145,778,000		1,162,332,000
Recognized gain on calls of securities held to maturity portfolio	2,000	16,000	15,000	30,000
Recognized loss on calls of securities held to maturity portfolio	0	0	0	2,000
Proceeds from the calls	2,415,000	13,269,000	8,810,000	22,478,000
Proceeds from maturities, calls and paydowns of investment securities held to maturity			24,481,000	51,146,000
Proceeds from sale of securities held to maturity portfolio		0
Number of securities in an unrealized loss position	333		333		270
PCI loans acquired	1,700,000		1,700,000
Available-for-sale Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Proceeds from maturities, calls and paydowns of securities available for sale	8,398,000
Gross losses	39,000		0
Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Number of securities in an unrealized loss position	1		1
Amortized cost	92,000		92,000
Unrealized losses			4,000
Nonperforming Financing Receivable [Member] | Held-to-maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Recognized gain on sale of securities held to maturity portfolio	3,000		18,000
Recognized loss on sale of securities held to maturity portfolio			0
Proceeds from maturities, calls and paydowns of investment securities held to maturity			$ 524,000