Stock-Based Compensation - Additional Information (Detail) (USD $)	9 Months Ended		3 Months Ended		9 Months Ended		1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Employee Stock Incentive Plan	Sep. 30, 2011 Employee Stock Incentive Plan	Sep. 30, 2012 Employee Stock Incentive Plan	Sep. 30, 2011 Employee Stock Incentive Plan	Sep. 30, 2012 State Bancorp's Stock Incentive Plan	Dec. 31, 2011 State Bancorp's Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, authorized			7,400,000		7,400,000
Number of shares, awarded during the period					544,000	15,000
Number of shares, available for grant			6,300,000		6,300,000
Stock-based compensation expense	$ 3,816,000	$ 2,535,000	$ 1,100,000	$ 1,200,000	$ 3,800,000	$ 2,500,000
Stock-based compensation amortization expense unrecognized					$ 4,300,000
Maximum vesting period, years					2 years
Assumed number of shares, outstanding								356,000
Outstanding stock options, weighted average exercise price							$ 17.41
Outstanding stock options, weighted average remaining term, in years							3 years
Number of shares, exercisable							321,000