Fair Value Disclosures - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial assets:
Investment securities available for sale	$ 789,125	$ 794,543
Investment securities held to maturity	163,611	164,346
Loans, held for sale	29,394	54,782
Loans, net	4,552,151	4,444,375
Impaired loans, net	62,443	46,499
Stock in FHLB of Pittsburgh	20,002	38,248
Accrued interest receivable	16,712	17,027
Other assets	81,793	84,892
Financial liabilities:
Deposits	5,376,830	4,738,438
Accrued interest payable	2,931	1,151
Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Loans, held for sale	0	0
Impaired loans, net	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Loans, held for sale	29,394	54,782
Impaired loans, net	0	0
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, held for sale	0	0
Impaired loans, net	62,443	46,499
Book Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	855,263	821,923
Book Value | Fair Value Inputs Level 1 And Level 2
Financial assets:
Investment securities available for sale	789,125	794,543
Book Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities held to maturity	163,611	164,346
Loans, held for sale	29,394	54,782
Stock in FHLB of Pittsburgh	20,002	38,248
Accrued interest receivable	16,712	17,027
Financial liabilities:
Deposits	5,376,830	4,738,438
Borrowed funds	700,849	1,267,447
Accrued interest payable	2,931	1,151
Other liabilities	3,194	3,380
Book Value | Fair Value Inputs Level 2 And Level 3
Financial assets:
Loans, net	4,489,708	4,397,876
Book Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Impaired loans, net	62,443	46,499
Other assets	13,920	9,189
Financial liabilities:
Standby letters of credit	507	468
Fair Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	855,263	821,923
Fair Value | Fair Value Inputs Level 1 And Level 2
Financial assets:
Investment securities available for sale	789,125	794,543
Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities held to maturity	163,241	163,232
Loans, held for sale	29,394	54,782
Stock in FHLB of Pittsburgh	20,002	38,248
Accrued interest receivable	16,712	17,027
Financial liabilities:
Deposits	5,040,211	4,423,921
Borrowed funds	697,952	1,264,170
Accrued interest payable	2,931	1,151
Other liabilities	3,194	3,380
Fair Value | Fair Value Inputs Level 2 And Level 3
Financial assets:
Loans, net	4,450,924	4,300,963
Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Impaired loans, net	62,443	46,499
Other assets	28,527	15,787
Financial liabilities:
Standby letters of credit	$ 507	$ 468