Investment Securities (Investment Securities Held to Maturity) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 478,846	$ 473,684
Gross unrealized gains	22,729	15,175
Gross unrealized losses	(140)	(528)
Fair value	501,435	488,331
Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	3,707	4,096
Gross unrealized gains	10	9
Gross unrealized losses	0	(8)
Fair value	3,717	4,097
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	1,192	1,597
Gross unrealized gains	49	61
Gross unrealized losses	0	0
Fair value	1,241	1,658
State And Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	464,556	458,062
Gross unrealized gains	22,618	15,094
Gross unrealized losses	(137)	(495)
Fair value	487,037	472,661
Corporate Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,391	9,929
Gross unrealized gains	52	11
Gross unrealized losses	(3)	(25)
Fair value	$ 9,440	$ 9,915