Junior Subordinated Debentures Issued to Capital Trusts - Additional Information (Detail) (USD $)	12 Months Ended				0 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Oct. 25, 2013	Jul. 26, 2013
Subordinated Borrowing [Line Items]
Net trading gains and losses included in non-cash credits			$ 881,000	$ 2,600,000
Junior subordinated debentures issued to capital trusts	41,252,000		41,089,000
Maximum allowable period of interest deferment	5 years
Percentage of securities issued by capital trusts	75.00%
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Redemption of related outstanding trust preferred securities					131,300,000
VNB Capital Trust I [Member]
Subordinated Borrowing [Line Items]
Contractual principal amounts redeemed of junior subordinated debentures						15,400,000
Debt instrument percentage						7.75%
GCB Capital Trust III [Member] | Trust Preferred Securities Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Debt instrument percentage	6.96%	[1]
Face value	24,000,000		24,000,000
GCB Capital Trust III [Member] | Subordinated Debentures Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Debt instrument percentage	6.96%	[1]
Junior subordinated debentures issued to capital trusts	24,914,000	[2]	25,000,000
Contractual principal balances	24,743,000		24,700,000
State Bancorp Capital Trust I [Member] | Trust Preferred Securities Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Face value	10,000,000		10,000,000
State Bancorp Capital Trust I [Member] | Subordinated Debentures Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debentures issued to capital trusts	8,524,000	[2]	8,400,000
Contractual principal balances	10,310,000		10,300,000
State Bancorp Capital Trust II [Member] | Trust Preferred Securities Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Face value	10,000,000		10,000,000
State Bancorp Capital Trust II [Member] | Subordinated Debentures Subject to Mandatory Redemption [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debentures issued to capital trusts	7,814,000	[2]	7,700,000
Contractual principal balances	$ 10,310,000		$ 10,300,000

[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.