Fair Value Disclosures - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financial assets:
Fair Value	$ 766,459	$ 721,029
Investment securities held-to-maturity	166,398	165,862
Loans, held-for-sale	32,625	41,807
Loans, net	3,801,240	3,729,050
Impaired loans, net	34,959	35,086
Reverse mortgage loans	25,263	24,284
Stock in FHLB of Pittsburgh	37,939	30,519
Accrued interest receivable	14,164	14,040
Other assets	57,817	66,715
Financial liabilities:
Deposits	3,992,139	4,016,566
Accrued interest payable	2,073	801
Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Loans, held-for-sale	32,625	41,807
Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Impaired loans, net	34,959	35,086
Book Value [Member]
Financial assets:
Fair Value	766,459	721,029
Loans, held-for-sale	32,625	41,807
Impaired loans, net	34,959	35,086
Book Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	703,893	561,179
Book Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Investment securities held-to-maturity	166,398	165,862
Loans, net	3,766,281	3,693,964
Stock in FHLB of Pittsburgh	37,939	30,519
Accrued interest receivable	14,164	14,040
Financial liabilities:
Deposits	3,992,139	4,016,566
Borrowed funds	1,168,802	932,886
Accrued interest payable	2,073	801
Book Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Reverse mortgage loans	25,263	24,284
Other assets	7,455	8,669
Financial liabilities:
Standby letters of credit	264	195
Fair Value [Member]
Financial assets:
Fair Value	766,459	721,029
Loans, held-for-sale	32,625	41,807
Impaired loans, net	34,959	35,086
Fair Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	703,893	561,179
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Investment securities held-to-maturity	173,032	167,743
Loans, net	3,752,905	3,637,714
Stock in FHLB of Pittsburgh	37,939	30,519
Accrued interest receivable	14,164	14,040
Financial liabilities:
Deposits	3,842,770	3,791,606
Borrowed funds	1,172,972	933,905
Accrued interest payable	2,073	801
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Reverse mortgage loans	25,263	24,284
Other assets	15,268	18,416
Financial liabilities:
Standby letters of credit	$ 264	$ 195