Fair Value Disclosures of Financial Assets - Book Value and Estimated Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financial assets:
Cash and cash equivalents	$ 530,612	$ 500,887	$ 459,695	$ 468,017
Loans held for sale	16,825	12,758
Loans, net	2,739,892	2,723,916
Stock in Federal Home Loan Bank of Pittsburgh	31,527	31,165
Accrued Interest receivable	10,028	9,652
Financial liabilities:
Deposits	3,188,519	3,274,963
Borrowed funds	33,895	28,945
Accrued interest payable	1,874	1,099
Book Value [Member]
Financial assets:
Investment securities	841,931	920,088
Book Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	530,612	500,887
Book Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Loans held for sale	16,825	12,758
Loans, net	2,739,892	2,723,916
Financial liabilities:
Standby letters of credit	167	224
Book Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Stock in Federal Home Loan Bank of Pittsburgh	31,527	31,165
Accrued Interest receivable	10,028	9,652
Financial liabilities:
Deposits	3,188,519	3,274,963
Borrowed funds	706,168	637,266
Accrued interest payable	1,874	1,099
Fair Value [Member]
Financial assets:
Investment securities	841,931	920,088
Fair Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	530,612	500,887
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Loans held for sale	16,825	12,758
Loans, net	2,755,066	2,746,001
Financial liabilities:
Standby letters of credit	167	224
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Stock in Federal Home Loan Bank of Pittsburgh	31,527	31,165
Accrued Interest receivable	10,028	9,652
Financial liabilities:
Deposits	3,055,822	3,174,907
Borrowed funds	706,988	638,375
Accrued interest payable	$ 1,874	$ 1,099