Investment Securities - Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 357,602	$ 357,500
Gross unrealized gains	8,274	5,753
Gross unrealized losses	(3,612)	(7,340)
Fair value	362,264	355,913
Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	7,175	7,523
Gross unrealized gains	19	13
Gross unrealized losses	(45)	(66)
Fair value	7,149	7,470
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	4,671	5,273
Gross unrealized gains	213	247
Gross unrealized losses	0	0
Fair value	4,884	5,520
State and Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	335,675	334,750
Gross unrealized gains	7,990	5,435
Gross unrealized losses	(3,523)	(7,198)
Fair value	340,142	332,987
Corporate Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	10,081	9,954
Gross unrealized gains	52	58
Gross unrealized losses	(44)	(76)
Fair value	$ 10,089	$ 9,936