Fair Value Disclosures - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial assets:
Fair Value	$ 774,712	$ 721,029
Investment securities held-to-maturity	166,962	165,862
Loans, held-for-sale	36,178	41,807
Loans, net	3,757,729	3,729,050
Impaired loans, net	33,701	35,086
Reverse mortgage loans	24,739	24,284
Stock in FHLB of Pittsburgh	30,711	30,519
Accrued interest receivable	13,992	14,040
Other assets	61,961	66,715
Financial liabilities:
Deposits	4,068,771	4,016,566
Accrued interest payable	1,340	801
Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Loans, held-for-sale	36,178	41,807
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Impaired loans, net	33,701	35,086
Book Value [Member]
Financial assets:
Fair Value	774,712	721,029
Loans, held-for-sale	36,178	41,807
Impaired loans, net	33,701	35,086
Book Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	590,028	561,179
Book Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Investment securities held-to-maturity	166,962	165,862
Loans, net	3,724,028	3,693,964
Stock in FHLB of Pittsburgh	30,711	30,519
Accrued interest receivable	13,992	14,040
Financial liabilities:
Deposits	4,068,771	4,016,566
Borrowed funds	971,264	932,886
Accrued interest payable	1,340	801
Book Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Reverse mortgage loans	24,739	24,284
Other assets	7,568	8,669
Financial liabilities:
Standby letters of credit	204	195
Fair Value [Member]
Financial assets:
Fair Value	774,712	721,029
Loans, held-for-sale	36,178	41,807
Impaired loans, net	33,701	35,086
Fair Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	590,028	561,179
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Investment securities held-to-maturity	170,540	167,743
Loans, net	3,685,174	3,637,714
Stock in FHLB of Pittsburgh	30,444	30,519
Accrued interest receivable	13,992	14,040
Financial liabilities:
Deposits	3,890,594	3,791,606
Borrowed funds	973,805	933,905
Accrued interest payable	1,340	801
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Reverse mortgage loans	24,739	24,284
Other assets	17,123	18,416
Financial liabilities:
Standby letters of credit	$ 204	$ 195