Investment Securities (Investment Securities Held to Maturity) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Recognized gain on calls of securities held to maturity portfolio	$ 5,000	$ 5,000	$ 0	$ 20,000
Amortized cost	471,723,000		471,723,000		$ 469,528,000
Gross unrealized gains	11,995,000		11,995,000		13,983,000
Gross unrealized losses	(1,223,000)		(1,223,000)		(1,038,000)
Fair value	482,495,000		482,495,000		482,473,000
Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	5,195,000		5,195,000		6,813,000
Gross unrealized gains	15,000		15,000		17,000
Gross unrealized losses	(1,000)		(1,000)		(20,000)
Fair value	5,209,000		5,209,000		6,810,000
Collateralized Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	1,821,000		1,821,000		2,816,000
Gross unrealized gains	78,000		78,000		123,000
Gross unrealized losses	0		0		0
Fair value	1,899,000		1,899,000		2,939,000
State And Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	454,446,000		454,446,000		449,410,000
Gross unrealized gains	11,870,000		11,870,000		13,814,000
Gross unrealized losses	(1,213,000)		(1,213,000)		(986,000)
Fair value	465,103,000		465,103,000		462,238,000
Corporate Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	10,261,000		10,261,000		10,489,000
Gross unrealized gains	32,000		32,000		29,000
Gross unrealized losses	(9,000)		(9,000)		(32,000)
Fair value	$ 10,284,000		$ 10,284,000		$ 10,486,000