Fair Value Disclosures of Financial Assets and Liabilities - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial assets:
Investment securities available for sale	$ 1,205,079	$ 837,499
Investment securities held to maturity	149,950	161,186
Other investments	37,233	17,971
Loans, held for sale	25,318	31,055
Loans, net	4,863,919	4,776,318
Stock in FHLB of Pittsburgh	19,259	31,284
Accrued interest receivable	22,001	19,405
Other assets	65,020	59,068
Financial liabilities:
Deposits	5,640,431	5,247,604
Accrued interest payable	1,900	1,037
Other liabilities	85,831	88,748
Fair Value
Financial assets:
Investment securities available for sale	1,205,079	837,499
Fair Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	620,757	723,866
Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities held to maturity	149,431	162,853
Loans, held for sale	25,318	31,055
Stock in FHLB of Pittsburgh	19,259	31,284
Accrued interest receivable	22,001	19,405
Financial liabilities:
Deposits	5,597,227	4,848,588
Borrowed funds	694,526	937,605
Accrued interest payable	1,900	1,037
Other liabilities	3,493	3,188
Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Other investments	37,233	45,326
Loans, net	4,772,377	4,699,458
Impaired loans, net	47,094	57,089
Other assets	2,098	2,883
Financial liabilities:
Standby letters of credit	495	603
Book Value
Financial assets:
Investment securities available for sale	1,205,079	837,499
Book Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	620,757	723,866
Book Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities held to maturity	149,950	161,186
Loans, held for sale	25,318	31,055
Stock in FHLB of Pittsburgh	19,259	31,284
Accrued interest receivable	22,001	19,405
Financial liabilities:
Deposits	5,640,431	5,247,604
Borrowed funds	699,788	937,806
Accrued interest payable	1,900	1,037
Other liabilities	3,493	3,188
Book Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Other investments	37,233	14,671
Loans, net	4,816,825	4,719,229
Impaired loans, net	47,094	57,089
Other assets	2,098	2,883
Financial liabilities:
Standby letters of credit	$ 495	$ 603