Fair Value Measurements - Book Value and Estimated Fair Value of Bank's Significant Financial Instruments Not Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Assets:
Debt securities held-to-maturity	$ 832,815	$ 761,660
Financial Liabilities:
Time deposits	866,244	607,104
Securities sold under agreements to repurchase with retail customers	61,760	79,668
Book Value
Financial Assets:
Cash and due from banks	120,792	109,613
Debt securities held-to-maturity	846,810	764,062
Restricted equity investments	56,784	19,724
Loans receivable, net and loans held-for-sale	5,579,222	3,966,014
Financial Liabilities:
Deposits other than time deposits	4,948,325	3,735,694
Time deposits	866,244	607,104
Federal Home Loan Bank advances and other borrowings	548,913	345,210
Level 1 Inputs
Financial Assets:
Cash and due from banks	120,792	109,613
Debt securities held-to-maturity	0	0
Financial Liabilities:
Securities sold under agreements to repurchase with retail customers	61,760	79,668
Level 2 Inputs
Financial Assets:
Debt securities held-to-maturity	830,999	751,182
Financial Liabilities:
Deposits other than time deposits	4,948,325	3,735,694
Time deposits	853,678	599,677
Federal Home Loan Bank advances and other borrowings	554,692	341,820
Level 3 Inputs
Financial Assets:
Debt securities held-to-maturity	1,816	10,478
Restricted equity investments	56,784	19,724
Loans receivable, net and loans held-for-sale	$ 5,474,306	$ 3,962,689