Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	$ 149,640	$ 101,522
Available-for-sale, Gross Unrealized Gains	1,413	163
Available-for-sale, Gross Unrealized Loss	(93)	(968)
Debt securities, available-for sale, at fair value	150,960	100,717
Held-to-maturity, Amortized Cost	772,975	851,903
Held-to-maturity, Gross Unrealized Gains	8,224	1,303
Held-to-maturity, Gross Unrealized Losses	(3,909)	(20,391)
Estimated Fair Value	777,290	832,815
Total, Amortized Cost	922,615	953,425
Total, Gross Unrealized Gains	9,637	1,466
Total, Gross Unrealized Losses	(4,002)	(21,359)
Total, Estimated Fair Value	928,250	933,532
Investment Securities
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	149,145
Available-for-sale, Gross Unrealized Gains	1,408
Available-for-sale, Gross Unrealized Loss	(93)
Debt securities, available-for sale, at fair value	150,460
Held-to-maturity, Amortized Cost	208,961	205,796
Held-to-maturity, Gross Unrealized Gains	2,384	193
Held-to-maturity, Gross Unrealized Losses	(2,629)	(6,811)
Estimated Fair Value	208,716	199,178
U.S. Agency Obligations \| Investment Securities
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	149,120	100,524
Available-for-sale, Gross Unrealized Gains	1,408	163
Available-for-sale, Gross Unrealized Loss	(93)	(963)
Debt securities, available-for sale, at fair value	150,435	99,724
Held-to-maturity, Amortized Cost	4,984	14,975
Held-to-maturity, Gross Unrealized Gains	14	0
Held-to-maturity, Gross Unrealized Losses	0	(130)
Estimated Fair Value	4,998	14,845
State and Municipal Obligations \| Investment Securities
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	25
Available-for-sale, Gross Unrealized Gains	0
Available-for-sale, Gross Unrealized Loss	0
Debt securities, available-for sale, at fair value	25
Held-to-maturity, Amortized Cost	124,430	123,987
Held-to-maturity, Gross Unrealized Gains	1,537	67
Held-to-maturity, Gross Unrealized Losses	(208)	(1,697)
Estimated Fair Value	125,759	122,357
Corporate Debt Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	39,836
Estimated Fair Value	37,628
Corporate Debt Securities \| Investment Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	79,547	66,834
Held-to-maturity, Gross Unrealized Gains	833	126
Held-to-maturity, Gross Unrealized Losses	(2,421)	(4,984)
Estimated Fair Value	77,959	61,976
Mortgage-Backed Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	564,014	646,107
Held-to-maturity, Gross Unrealized Gains	5,840	1,110
Held-to-maturity, Gross Unrealized Losses	(1,280)	(13,580)
Estimated Fair Value	568,574	633,637
Mortgage-Backed Securities \| FNMA
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	495	998
Available-for-sale, Gross Unrealized Gains	5	0
Available-for-sale, Gross Unrealized Loss	0	(5)
Debt securities, available-for sale, at fair value	500	993
Held-to-maturity, Amortized Cost	244,428	277,266
Held-to-maturity, Gross Unrealized Gains	2,680	753
Held-to-maturity, Gross Unrealized Losses	(493)	(6,030)
Estimated Fair Value	246,615	271,989
Mortgage-Backed Securities \| FHLMC
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	206,985	237,703
Held-to-maturity, Gross Unrealized Gains	2,221	159
Held-to-maturity, Gross Unrealized Losses	(524)	(5,110)
Estimated Fair Value	208,682	232,752
Mortgage-Backed Securities \| GNMA
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	110,661	127,611
Held-to-maturity, Gross Unrealized Gains	939	198
Held-to-maturity, Gross Unrealized Losses	(212)	(2,360)
Estimated Fair Value	111,388	125,449
Mortgage-Backed Securities \| SBA
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	1,940	3,527
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized Losses	(51)	(80)
Estimated Fair Value	$ 1,889	$ 3,447

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