Gross Unrealized Losses and Fair Value by Length of Time of Available-For-Sale Securities (Detail) (Available-for-Sale Securities, USD $) In Thousands, unless otherwise specified	Sep. 30, 2013 Securities	Dec. 31, 2012 Securities
Schedule of Available-for-sale Securities [Line Items]
Number of securities	46	7
Fair Value	$ 295,890	$ 46,404
Less than 12 months	10,669	231
More than 12 months	262	236
Total Unrealized Losses	10,931	467
U.S. Government Agencies
Schedule of Available-for-sale Securities [Line Items]
Number of securities	14	2
Fair Value	138,520	29,900
Less than 12 months	5,862	98
More than 12 months	0	0
Total Unrealized Losses	5,862	98
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Number of securities	7	1
Fair Value	5,758	390
Less than 12 months	70	1
More than 12 months	0	0
Total Unrealized Losses	70	1
Mortgage-Backed
Schedule of Available-for-sale Securities [Line Items]
Number of securities	24	2
Fair Value	150,173	12,653
Less than 12 months	4,737	128
More than 12 months	0	0
Total Unrealized Losses	4,737	128
Trust Preferred
Schedule of Available-for-sale Securities [Line Items]
Number of securities	1	1
Fair Value	1,439	1,465
Less than 12 months	0	0
More than 12 months	262	236
Total Unrealized Losses	262	236
Corporate Debt
Schedule of Available-for-sale Securities [Line Items]
Number of securities		1
Fair Value		1,996
Less than 12 months		4
More than 12 months		0
Total Unrealized Losses		$ 4