Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended									12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Residential Mortgage Loans [Member]	Dec. 31, 2011 Residential Mortgage Loans [Member]	Dec. 31, 2010 Residential Mortgage Loans [Member]	Dec. 31, 2012 SBA Loans [Member]	Dec. 31, 2011 SBA Loans [Member]	Dec. 31, 2010 SBA Loans [Member]	Dec. 31, 2012 Core deposits [member]	Mar. 31, 2012 Core deposits [member] State Bancorp, Inc.[Member]	Dec. 31, 2012 Other [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill recorded	$ 110,272,000	$ 71,000
Goodwill impairment	0	0	0
Aggregate principal balances of mortgage loans serviced				1,800,000,000	1,300,000,000	1,300,000,000
Total amount of loans serviced by bank							30,400,000	33,100,000	38,400,000
Weighted average amortization period, years										10 years		17 years
Core deposits intangibles from acquisition											8,100,000
Impairment of core deposits and intangibles	0	0	0
Amortization expense - other intangible assets	$ 9,800,000	$ 9,300,000	$ 7,700,000