Business Combinations (FDIC Assisted Transactions) (Detail) (USD $)	3 Months Ended		14 Months Ended	24 Months Ended		0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 financial_institution	Dec. 31, 2011 financial_institution	Dec. 31, 2012	Feb. 10, 2012 Charter National [Member]	Jul. 20, 2012 Second Federal [Member]		Sep. 28, 2012 First United Bank [Member]	Feb. 01, 2013 Second Federal [Member]
Business Acquisition [Line Items]
Divestiture of Businesses, Deposits Disposed										$ 149,000,000
Number of FDIC assisted banks acquired			3	6
Business Acquisition, Effective Date of Acquisition						Feb. 10, 2012	Jul. 20, 2012		Sep. 28, 2012
Fair value of assets acquired, at the acquisition date						92,355,000	171,625,000		328,408,000
Fair value of loans acquired, at the acquisition date						45,555,000	0		77,964,000
Fair value of liabilities assumed, at the acquisition date						91,570,000	171,582,000		321,734,000
Fair value of reimbursable losses, at the acquisition date	170,696,000	263,212,000	170,696,000	344,251,000	208,160,000	13,164,000	0	[1]	67,190,000
Gain on bargain purchase recognized	$ 0	$ 840,000				$ 785,000	$ 43,000		$ 6,675,000
FDIC loss sharing percentage on purchased loans, OREO, and certain other assets	80.00%

[1] As no assets subject to loss sharing agreements were acquired in the acquisition of Second Federal, there was no fair value of reimbursable losses.