Fair Value Measurements - Book Value and Estimated Fair Value of Bank's Significant Financial Instruments Not Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial Assets:
Debt securities held-to-maturity	$ 869,167	$ 832,815
Restricted equity investments, at cost	59,425	56,784
Financial Liabilities:
Time deposits	921,921	866,244
Securities sold under agreements to repurchase with retail customers	62,086	61,760
Book Value
Financial Assets:
Cash and due from banks	148,327	120,792
Debt securities held-to-maturity	863,838	846,810
Restricted equity investments, at cost	59,425	56,784
Loans receivable, net and loans held-for-sale	5,943,930	5,579,222
Financial Liabilities:
Deposits other than time deposits	5,265,566	4,948,325
Time deposits	921,921	866,244
Federal Home Loan Bank advances and other borrowings	550,179	548,913
Securities sold under agreements to repurchase with retail customers	62,086	61,760
Level 1 Inputs
Financial Assets:
Cash and due from banks	148,327	120,792
Debt securities held-to-maturity	0	0
Restricted equity investments, at cost	0	0
Loans receivable, net and loans held-for-sale	0	0
Financial Liabilities:
Deposits other than time deposits	0	0
Time deposits	0	0
Federal Home Loan Bank advances and other borrowings	0	0
Securities sold under agreements to repurchase with retail customers	62,086	61,760
Level 2 Inputs
Financial Assets:
Cash and due from banks	0	0
Debt securities held-to-maturity	859,032	830,999
Restricted equity investments, at cost	0	0
Loans receivable, net and loans held-for-sale	0	0
Financial Liabilities:
Deposits other than time deposits	5,265,566	4,948,325
Time deposits	919,780	853,678
Federal Home Loan Bank advances and other borrowings	560,340	554,692
Securities sold under agreements to repurchase with retail customers	0	0
Level 3 Inputs
Financial Assets:
Cash and due from banks	0	0
Debt securities held-to-maturity	10,135	1,816
Restricted equity investments, at cost	59,425	56,784
Loans receivable, net and loans held-for-sale	5,981,956	5,474,306
Financial Liabilities:
Deposits other than time deposits	0	0
Time deposits	0	0
Federal Home Loan Bank advances and other borrowings	0	0
Securities sold under agreements to repurchase with retail customers	$ 0	$ 0