Fair Value Disclosures of Financial Assets and Liabilities - Book Value and Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Investment securities available for sale	$ 1,944,914	$ 1,205,079
Investment securities held to maturity	133,601	149,950
Loans, net	8,424,464	4,863,919
Stock in FHLB of Pittsburgh	21,097	19,259
Accrued interest receivable	38,094	22,001
Financial liabilities:
Deposits	9,586,857	5,640,431
Accrued interest payable	3,103	1,900
Fair Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	571,752	620,757
Fair Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities available for sale	1,944,914	1,205,079
Investment securities held to maturity	136,625	149,431
Loans, held for sale	83,872	25,318
Stock in FHLB of Pittsburgh	21,097	19,259
Accrued interest receivable	38,094	22,001
Other assets	4,884	2,098
Financial liabilities:
Deposits	9,575,394	5,597,227
Borrowed funds	489,561	694,526
Accrued interest payable	3,103	1,900
Other liabilities	3,918	3,493
Fair Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Other investments	70,046	37,233
Loans, net	8,537,735	4,772,377
Collateral for collateral dependent loans	42,280	47,094
Financial liabilities:
Standby letters of credit	623	495
Book Value | Quoted Prices in Active Markets for Identical Asset (Level 1)
Financial assets:
Cash and cash equivalents	571,752	620,757
Book Value | Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities available for sale	1,944,914	1,205,079
Investment securities held to maturity	133,601	149,950
Loans, held for sale	83,872	25,318
Stock in FHLB of Pittsburgh	21,097	19,259
Accrued interest receivable	38,094	22,001
Other assets	4,884	2,098
Financial liabilities:
Deposits	9,586,857	5,640,431
Borrowed funds	489,288	699,788
Accrued interest payable	3,103	1,900
Other liabilities	3,918	3,493
Book Value | Significant Unobservable Inputs (Level 3)
Financial assets:
Other investments	70,046	37,233
Loans, net	8,382,184	4,816,825
Collateral for collateral dependent loans	42,280	47,094
Financial liabilities:
Standby letters of credit	$ 623	$ 495