Securities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 Security	Sep. 30, 2012	Dec. 31, 2012
Schedule Of Securities [Line Items]
Securities pledged to secure public deposits, trust deposits and for other purposes, carrying value	$ 1,025,579		$ 725,450
Securities pledged as collateral for short-term borrowings, carrying value	849,901		795,812
Recover rate of banks	10.00%
Recover rate of insurance companies	15.00%
Number of pooled issue securities	23
Number of single-issuer securities	4
Estimated fair value of pooled trust preferred securities	28,704
Estimated fair value of single-issue trust preferred securities	5,963
Accretion income recognized by Corporation	2,448	2,138
Number of current pooled trust preferred securities	4
Remaining non-accrual pooled trust preferred securities	2
Accruing pooled trust preferred securities	3
Number of pooled securities accreting income	18
Additional accretion income recognized		34
Impairment losses on securities	0	119
Municipal bond portfolio, value	152,922
Percent of municipal bond portfolio rated A or better	98.70%
Percent of municipal bond portfolio, general obligation bonds	99.00%
Percent of municipal bonds from Pennsylvania	78.00%
Average holding size of municipal bond	$ 987
Percent of portfolio with credit support	67.70%
Preferred Trust Securities [Member]
Schedule Of Securities [Line Items]
Number of pooled trust preferred securities sold		2
Senior Tranches [Member]
Schedule Of Securities [Line Items]
Number of single-issuer securities	2
Mezzanine Tranches [Member]
Schedule Of Securities [Line Items]
Number of pooled issue securities	21
Minimum [Member]
Schedule Of Securities [Line Items]
Deferral rates after the deferral period ends	10.00%
Maximum [Member]
Schedule Of Securities [Line Items]
Deferral rates after the deferral period ends	90.00%