Fair Value Disclosures - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Financial assets:
Cash and cash equivalents	$ 533,691	$ 508,039	$ 475,189	$ 484,426
Fair Value	781,746	740,124
Investment securities held-to-maturity	120,697	126,168
Loans, held-for-sale	48,099	28,508
Loans, net	3,295,471	3,156,652
Reverse mortgage loans	25,945	29,298
Stock in FHLB of Pittsburgh	31,832	23,278
Accrued interest receivable	12,272	11,782
Other assets	54,125	54,561
Financial liabilities:
Deposits	3,526,455	3,649,235
Accrued interest payable	1,879	1,004
Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Loans, held-for-sale	48,099	28,508
Book Value [Member]
Financial assets:
Fair Value	781,746	740,124
Investment securities held-to-maturity	120,697	126,168
Loans, held-for-sale	48,099	28,508
Book Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	533,691	508,039
Book Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Loans, net	3,295,471	3,156,652
Stock in FHLB of Pittsburgh	31,832	23,278
Accrued interest receivable	12,272	11,782
Financial liabilities:
Deposits	3,526,455	3,649,235
Borrowed funds	1,000,900	667,775
Accrued interest payable	1,879	1,004
Book Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Reverse mortgage loans	25,945	29,298
Financial liabilities:
Standby letters of credit	208	151
Fair Value [Member]
Financial assets:
Fair Value	781,746	740,124
Investment securities held-to-maturity	118,804	126,171
Loans, held-for-sale	48,099	28,508
Fair Value [Member] | Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Financial assets:
Cash and cash equivalents	533,691	508,039
Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets:
Loans, net	3,255,521	3,121,855
Stock in FHLB of Pittsburgh	31,832	23,278
Accrued interest receivable	12,272	11,782
Financial liabilities:
Deposits	3,324,400	3,461,218
Borrowed funds	1,002,993	672,850
Accrued interest payable	1,879	1,004
Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets:
Reverse mortgage loans	25,945	29,298
Other assets	4,971	4,837
Financial liabilities:
Standby letters of credit	$ 208	$ 151