Junior Subordinated Debentures Issued to Capital Trusts - Schedule of Outstanding Junior Subordinated Debentures and Related Trust Preferred Securities Issued by Each Trust (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	$ 41,252,000		$ 41,089,000
GCB Capital Trust III [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Annual interest rate, base rate	3-month LIBOR
Annual interest rate spread, percentage	1.40%
Trust Preferred Securities Subject to Mandatory Redemption [Member] | State Bancorp Capital Trust I [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Face value	10,000,000		10,000,000
Annual interest rate, base rate	3-month LIBOR	[1]
Annual interest rate spread, percentage	3.45%	[1]
Issuance date	October 29, 2002
Distribution dates	Quarterly
Trust Preferred Securities Subject to Mandatory Redemption [Member] | State Bancorp Capital Trust II [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Face value	10,000,000		10,000,000
Annual interest rate, base rate	3-month LIBOR	[1]
Annual interest rate spread, percentage	2.85%	[1]
Issuance date	December 19, 2003
Distribution dates	Quarterly
Trust Preferred Securities Subject to Mandatory Redemption [Member] | GCB Capital Trust III [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Face value	24,000,000		24,000,000
Annual interest rate	6.96%	[1]
Issuance date	July 2, 2007
Distribution dates	Quarterly
Subordinated Debentures Subject to Mandatory Redemption [Member] | State Bancorp Capital Trust I [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	8,524,000	[2]	8,400,000
Contractual principal balance	10,310,000		10,300,000
Annual interest rate, base rate	3-month LIBOR	[1]
Annual interest rate spread, percentage	3.45%	[1]
Stated maturity date	Nov. 07, 2032
Initial call date	Nov. 07, 2007
Subordinated Debentures Subject to Mandatory Redemption [Member] | State Bancorp Capital Trust II [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	7,814,000	[2]	7,700,000
Contractual principal balance	10,310,000		10,300,000
Annual interest rate, base rate	3-month LIBOR	[1]
Annual interest rate spread, percentage	2.85%	[1]
Stated maturity date	Jan. 23, 2034
Initial call date	Jan. 23, 2009
Subordinated Debentures Subject to Mandatory Redemption [Member] | GCB Capital Trust III [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	24,914,000	[2]	25,000,000
Contractual principal balance	$ 24,743,000		$ 24,700,000
Annual interest rate	6.96%	[1]
Stated maturity date	Jul. 30, 2037
Initial call date	Jul. 30, 2017

[1] Interest on GCB Capital Trust III is fixed until July 30, 2017, then resets to 3-month LIBOR plus 1.4 percent. The annual interest rate for all of the junior subordinated debentures and related trust preferred securities excludes the effect of the purchase accounting adjustments.

[2] The carrying value for GCB Capital Trust III includes an unamortized purchase accounting premium of $171 thousand, and the carrying values for State Bancorp Capital Trust I and State Bancorp Capital Trust II include purchase accounting discounts of $1.8 million and $2.5 million, respectively.