Business Combinations and Dispositions - Additional Information (Detail) (USD $) Share data in Thousands, unless otherwise specified	3 Months Ended												12 Months Ended					12 Months Ended									1 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 14, 2010 Y	Mar. 12, 2010	Dec. 31, 2011 New York Network [Member] Branch	Dec. 31, 2012 Short-term borrowings [Member]	Dec. 31, 2011 State Bancorp, Inc.[Member] Branch	Dec. 31, 2011 State Bancorp, Inc.[Member] New York Network [Member] Branch	Dec. 31, 2011 State Bancorp, Inc.[Member] Other New York Locations [Member] Branch	Mar. 12, 2010 LibertyPointe Bank Acquisition [Member]	Mar. 11, 2010 LibertyPointe Bank Acquisition [Member]	Dec. 31, 2012 Park Avenue Bank Acquisition [Member]	Mar. 12, 2010 Park Avenue Bank Acquisition [Member]	Dec. 14, 2010 S&M Klein Co. Inc. [Member]
Business Acquisition [Line Items]
Acquisition date																				Jan. 01, 2012
Assets																				$ 1,686,354,000
Loans																				1,088,421,000
Deposits																				1,380,293,000
Number of branches acquired																				16	15	5
Number of branches in network																		44
Total estimated consideration for the acquisition																				208,000,000							3,300,000
Fixed Rate Cumulative Series A Preferred Stock redeemed, value					36,800,000									36,800,000
Short term loan for stock redemption					37,000,000									37,000,000
Number of years purchase warrant can be used														10
Number of common stock issued upon exercise of warrant													489	489
Exercise price of warrant	11.30				11.30								11.30	11.30
Merger expenses													1,100,000
Professional and legal fees													15,005,000	15,312,000	10,137,000					1,700,000
Employee benefits expense																				640,000
Non-interest expense	95,623,000	93,219,000	91,510,000	94,548,000	84,869,000	[1]	85,794,000	[1]	83,572,000	[1]	84,321,000	[1]	374,900,000	338,556,000	319,688,000					290,000
Estimated useful life													11 years
Debentures, maturity date																			Mar. 01, 2012
Total deposits assumed in FDIC assisted bank acquisitions																								198,300,000		455,900,000
Total assets acquired																								207,700,000		480,500,000
Covered loans																								140,600,000		271,800,000
Goodwill	428,234,000				317,962,000								428,234,000	317,962,000	317,891,000									11,600,000		7,900,000
Estimated consideration for the acquisition of intangible assets																								370,000		1,200,000	3,300,000
FDIC loss share coverage percentage up to first tranche																							80.00%			80.00%
FDIC loss share recovery limit first tranche																							55,000,000			66,000,000
Portion of first loss tranche ineligible for FDIC reimbursement																							11,700,000
FDIC loss share coverage percentage up to first tranche																							95.00%			95.00%
First tranche reimbursement percentage from bank FDIC																	80.00%
Second tranche reimbursement percentage from bank to FDIC															95.00%
Cash settled equity instrument exercise date																									April 1, 2010
Purchase price of acquisition																											5,300,000
Total earn-out payments																											2,000,000
Goodwill																				$ 109,758,000							$ 1,900,000
Weighted average amortization period, years																											16 years
Purchase price payable period years																4

[1] Previously reported amounts have been revised to reflect an increase in non-interest expense due to the immaterial correction of an error. See the "Correction of an Immaterial Error" section of Note 1 to the consolidated financial statements for additional information.