Junior Subordinated Debentures Issued to Capital Trusts - Schedule of Outstanding Junior Subordinated Debentures and Related Trust Preferred Securities Issued by Each Trust non-printing (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
State Bancorp Capital Trust I [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Purchase accounting discounts	$ 1,800,000
State Bancorp Capital Trust II [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Purchase accounting discounts	2,500,000
GCB Capital Trust III [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Unamortized purchase accounting premium	$ 171,000
Annual interest rate, base rate	3-month LIBOR
Annual interest rate spread, percentage	1.40%