Investment Securities (Narrative) (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) position security	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) position security	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) position security
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 1,032,235,000		$ 1,032,235,000		$ 964,534,000
Investment securities held to maturity	$ 476,359,000		$ 476,359,000		$ 473,684,000
Total number of all held to maturity and available for sale securities in an unrealized loss position | security	76		76		163
Amortized cost	$ 1,011,433,000		$ 1,011,433,000		$ 957,938,000
Proceeds from the sale of securities available for sale	1,200,000	$ 0	3,400,000
Gross gains	0		95,000	$ 643,000
Gross losses	$ 45,000		45,000	0
Proceeds from maturities, prepayments and calls of short-term investments				14,000,000
Proceeds from calls on securities available for sale			$ 0	465,000
Recognized gain on calls of securities				2,000
Number of securities in an unrealized loss position | position	16		16		64
Other-than-temporary impairment charges, net	$ 0		$ 0
Proceeds from calls of held to maturity securities	20,300,000	8,000,000	35,200,000	21,200,000
Recognized gain on calls of securities, held-to-maturity portfolio	2,000		4,000	5,000
Recognized loss on calls of securities held-to-maturity portfolio	0	$ 0	0	$ 0
Held-to-maturity securities, fair value	$ 495,516,000		$ 495,516,000		$ 488,331,000
Number of securities in an unrealized loss position | position	60		60		99
Private Label Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 523,000		$ 523,000
Number of securities in an unrealized loss position | position	3		3
Unrealized losses			$ 6,000
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	$ 935,781,000		935,781,000		$ 863,861,000
Investment securities held to maturity	1,037,000		1,037,000		1,597,000
Amortized cost	915,693,000		915,693,000		857,430,000
Held-to-maturity securities, amortized cost	1,000,000		1,000,000
Held-to-maturity securities, fair value	1,079,000		1,079,000		1,658,000
Equity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities available for sale, at fair value	548,000		548,000		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	0		0