Fair Value Measurement - Estimates Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financial Assets
Cash and due from banks	$ 155,559	$ 117,572
Equity securities	13,494	13,457
Debt securities available-for-sale	1,796,571	1,261,865
Debt securities held-to-maturity	1,019,746	1,009,500
Net loans	6,745,261	6,296,157
Loans held for sale	12,053	20,320
Accrued interest receivable	33,868	29,728
Financial Liabilities
Deposits	7,668,604	7,043,588
Federal Home Loan Bank borrowings	1,248,406	948,203
Other borrowings	258,067	184,805
Subordinated debt and junior subordinated debt	165,420	164,327
Accrued interest payable	4,417	3,178
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial Assets
Cash and due from banks	155,559	117,572
Equity securities	13,494	11,391
Accrued interest receivable	33,868	29,728
Financial Liabilities
Deposits	6,292,076	5,766,531
Other borrowings	256,069	182,785
Accrued interest payable	4,417	3,178
Significant Other Observable Inputs (Level 2) [Member]
Financial Assets
Cash and due from banks	0
Debt securities available-for-sale	1,796,571	1,261,865
Debt securities held-to-maturity	1,015,540	1,023,191
Loans held for sale	12,053	20,320
Other assets - interest rate derivatives	11,048	7,351
Financial Liabilities
Deposits	1,386,749	1,287,005
Federal Home Loan Bank borrowings	1,240,239	944,706
Other borrowings	1,988	2,029
Subordinated debt and junior subordinated debt	153,405	146,484
Other liabilities - interest rate derivatives	10,832	7,345
Accrued interest payable	0
Significant Unobservable Inputs (Level 3) [Member]
Financial Assets
Cash and due from banks	0
Debt securities held-to-maturity	571	593
Net loans	6,647,280	6,212,823
Financial Liabilities
Accrued interest payable	0
Carrying Amount [Member]
Financial Assets
Cash and due from banks	155,559	117,572
Equity securities	13,494	13,457
Debt securities available-for-sale	1,796,571	1,261,865
Debt securities held-to-maturity	1,019,746	1,009,500
Net loans	6,745,261	6,296,157
Loans held for sale	12,053	20,320
Other assets - interest rate derivatives	11,048	7,351
Accrued interest receivable	33,868	29,728
Financial Liabilities
Deposits	7,668,604	7,043,588
Federal Home Loan Bank borrowings	1,248,406	948,203
Other borrowings	258,067	184,805
Subordinated debt and junior subordinated debt	165,420	164,327
Other liabilities - interest rate derivatives	10,832	7,345
Accrued interest payable	4,417	3,178
Fair Value Estimate [Member]
Financial Assets
Cash and due from banks	155,559	117,572
Equity securities	13,494	13,457
Debt securities available-for-sale	1,796,571	1,261,865
Debt securities held-to-maturity	1,016,111	1,023,784
Net loans	6,647,280	6,212,823
Loans held for sale	12,053	20,320
Other assets - interest rate derivatives	11,048	7,351
Accrued interest receivable	33,868	29,728
Financial Liabilities
Deposits	7,678,825	7,053,536
Federal Home Loan Bank borrowings	1,240,239	944,706
Other borrowings	258,057	184,814
Subordinated debt and junior subordinated debt	153,405	146,484
Other liabilities - interest rate derivatives	10,832	7,345
Accrued interest payable	4,417	3,178
Investments Measured at Net Asset Value [Member]
Financial Assets
Cash and due from banks	0
Equity securities		$ 2,066
Financial Liabilities
Accrued interest payable	$ 0