Loans and Leases (Schedule of Changes in Accretable Discount Related to Credit Impaired Acquired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Changes In Accretable Discount [Line Items]
Balance - beginning of period	$ 62,868	$ 4,881
Tower acquisition	0	54,418
Accretion recognized during the period	(6,570)	(2,500)
Net reclassification from non-accretable to accretable	2,519	0
Balance - end of period	$ 58,817	$ 56,799