Business Combinations - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended	9 Months Ended		9 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Short-term Debt [Member]	Jun. 30, 2012 State Bancorp, Inc.	Dec. 31, 2011 State Bancorp, Inc.
Business Acquisition [Line Items]
Assets	$ 15,771,134,000		$ 15,771,134,000	$ 14,244,507,000			$ 1,700,000,000
Number of branches							16
Acquisition date		Jan. 01, 2012
Exchange ratio for one common stock		1
Total estimated consideration for the acquisition						208,400,000
Number of shares issued in acquisition						17,700,000
Fixed Rate Cumulative Series A Preferred Stock redeemed, value		36,800,000
Short-term loan for stock redemption		37,000,000
Assumed junior subordinated debentures	190,594,000		190,594,000	185,598,000		20,600,000
Debentures, maturity date		Nov. 07, 2032			Mar. 01, 2012
Trust preferred securities, maturity date		Jan. 23, 2034
Number of years purchase warrant can be used			10
Number of common stock issued upon exercise of warrant			489,000
Exercise price of warrants	11.30		11.30
Merger expenses	$ 40,000		$ 1,100,000
Estimated useful life			11 years