FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial assets:
Investment securities available for sale	$ 907,818	$ 837,499
Investment securities held to maturity	159,672	161,186
Other investments	33,363	17,971
Loans, held for sale	15,937	31,055
Loans, net	4,805,758	4,776,318
Stock in FHLB of Pittsburgh	28,854	31,284
Accrued interest receivable	19,969	19,405
Other assets	61,200	59,068
Financial liabilities:
Deposits	5,202,515	5,247,604
Accrued interest payable	3,450	1,037
Book Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	711,089	723,866
Book Value | Fair Value Inputs Level 1 And Level 2
Financial assets:
Investment securities available for sale	907,818	837,499
Book Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities held to maturity	159,672	161,186
Loans, held for sale	15,937	31,055
Stock in FHLB of Pittsburgh	28,854	31,284
Accrued interest receivable	19,969	19,405
Financial liabilities:
Deposits	5,202,515	5,247,604
Borrowed funds	932,197	937,806
Accrued interest payable	3,450	1,037
Other liabilities	4,335	3,188
Book Value | Fair Value Inputs Level 1 And Level 3
Financial assets:
Other investments	33,363	17,971
Book Value | Fair Value Inputs Level 2 And Level 3
Financial assets:
Loans, net	4,749,604	4,719,229
Book Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Impaired loans, net	56,154	57,089
Other assets	1,606	790
Financial liabilities:
Standby letters of credit	562	603
Fair Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	711,089	723,866
Fair Value | Fair Value Inputs Level 1 And Level 2
Financial assets:
Investment securities available for sale	907,818	837,499
Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities held to maturity	159,164	162,853
Loans, held for sale	15,937	31,055
Stock in FHLB of Pittsburgh	28,854	31,284
Accrued interest receivable	19,969	19,405
Financial liabilities:
Deposits	4,768,066	4,848,588
Borrowed funds	925,902	937,605
Accrued interest payable	3,450	1,037
Other liabilities	4,335	3,188
Fair Value | Fair Value Inputs Level 1 And Level 3
Financial assets:
Other investments	33,363	48,050
Fair Value | Fair Value Inputs Level 2 And Level 3
Financial assets:
Loans, net	4,732,340	4,699,458
Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Impaired loans, net	56,154	57,089
Other assets	1,606	790
Financial liabilities:
Standby letters of credit	$ 562	$ 603