Junior Subordinated Debentures Issued to Capital Trusts - Schedule of Outstanding Junior Subordinated Debentures and Related Trust Preferred Securities Issued by Each Trust (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	$ 41,577	$ 41,414
GCB Capital Trust III | 3-month LIBOR
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Annual interest rate spread, percentage	1.40%
Junior Subordinated Debentures: | GCB Capital Trust III
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	$ 24,777	24,846
Contractual principal balance	$ 24,743	24,743
Annual interest rate	6.96%
Junior Subordinated Debentures: | State Bancorp Capital Trust I
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	$ 8,724	8,624
Contractual principal balance	$ 10,310	10,310
Junior Subordinated Debentures: | State Bancorp Capital Trust I | 3-month LIBOR
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Annual interest rate spread, percentage	3.45%
Junior Subordinated Debentures: | State Bancorp Capital Trust II
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Carrying value	$ 8,076	7,944
Contractual principal balance	$ 10,310	10,310
Junior Subordinated Debentures: | State Bancorp Capital Trust II | 3-month LIBOR
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Annual interest rate spread, percentage	2.85%
Trust Preferred Securities: | GCB Capital Trust III
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Face value	$ 24,000	24,000
Annual interest rate	6.96%
Trust Preferred Securities: | State Bancorp Capital Trust I
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Face value	$ 10,000	10,000
Trust Preferred Securities: | State Bancorp Capital Trust I | 3-month LIBOR
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Annual interest rate spread, percentage	3.45%
Trust Preferred Securities: | State Bancorp Capital Trust II
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Face value	$ 10,000	$ 10,000
Trust Preferred Securities: | State Bancorp Capital Trust II | 3-month LIBOR
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Annual interest rate spread, percentage	2.85%