Securities - Estimated Fair Value and Unrealized Loss for Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available-for-sale, Less than 12 months, Estimated Fair Value	$ 25,021	$ 1,978
Available-for-sale, Less than 12 months, Unrealized Losses	(54)	(8)
Available-for-sale, 12 months or Longer, Estimated Fair Value	22,451	66,438
Available-for-sale, 12 months or longer, Unrealized Losses	(39)	(960)
Available-for-sale, Total, Estimated Fair Value	47,472	68,416
Available-for-sale, Total, Unrealized Losses	(93)	(968)
Held-to-maturity, Less than 12 months, Estimated Fair Value	67,314	118,203
Held-to-maturity, Less than 12 months, Unrealized Losses	(452)	(924)
Held-to-maturity, 12 months or longer, Estimated Fair Value	151,085	556,536
Held-to-maturity, 12 months or longer, Unrealized Losses	(3,457)	(19,467)
Held-to-maturity, Total, Estimated Fair Value	218,399	674,739
Held-to-maturity, Total, Unrealized Losses	(3,909)	(20,391)
Total securities, Less than 12 months, Estimated Fair Value	92,335	120,181
Total securities, Less than 12 months, Unrealized Losses	(506)	(932)
Total securities, 12 months or longer, Estimated Fair Value	173,536	622,974
Total securities, 12 months or longer, Unrealized Losses	(3,496)	(20,427)
Total securities, Estimated Fair Value	265,871	743,155
Total securities, Unrealized Losses	(4,002)	(21,359)
Other investments
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available-for-sale, Less than 12 months, Estimated Fair Value		993
Available-for-sale, Less than 12 months, Unrealized Losses		(5)
Available-for-sale, 12 months or Longer, Estimated Fair Value		0
Available-for-sale, 12 months or longer, Unrealized Losses		0
Available-for-sale, Total, Estimated Fair Value		993
Available-for-sale, Total, Unrealized Losses		(5)
Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	50,279	112,877
Held-to-maturity, Less than 12 months, Unrealized Losses	(181)	(899)
Held-to-maturity, 12 months or longer, Estimated Fair Value	98,926	392,559
Held-to-maturity, 12 months or longer, Unrealized Losses	(1,099)	(12,681)
Held-to-maturity, Total, Estimated Fair Value	149,205	505,436
Held-to-maturity, Total, Unrealized Losses	(1,280)	(13,580)
Investment Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	17,035	5,326
Held-to-maturity, Less than 12 months, Unrealized Losses	(271)	(25)
Held-to-maturity, 12 months or longer, Estimated Fair Value	52,159	163,977
Held-to-maturity, 12 months or longer, Unrealized Losses	(2,358)	(6,786)
Held-to-maturity, Total, Estimated Fair Value	69,194	169,303
Held-to-maturity, Total, Unrealized Losses	(2,629)	(6,811)
Investment Securities | U.S. Agency Obligations
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available-for-sale, Less than 12 months, Estimated Fair Value	25,021	985
Available-for-sale, Less than 12 months, Unrealized Losses	(54)	(3)
Available-for-sale, 12 months or Longer, Estimated Fair Value	22,451	66,438
Available-for-sale, 12 months or longer, Unrealized Losses	(39)	(960)
Available-for-sale, Total, Estimated Fair Value	47,472	67,423
Available-for-sale, Total, Unrealized Losses	(93)	(963)
Held-to-maturity, Less than 12 months, Estimated Fair Value		0
Held-to-maturity, Less than 12 months, Unrealized Losses		0
Held-to-maturity, 12 months or longer, Estimated Fair Value		14,845
Held-to-maturity, 12 months or longer, Unrealized Losses		(130)
Held-to-maturity, Total, Estimated Fair Value		14,845
Held-to-maturity, Total, Unrealized Losses	0	(130)
Investment Securities | State and Municipal Obligations
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	7,308	2,856
Held-to-maturity, Less than 12 months, Unrealized Losses	(58)	(4)
Held-to-maturity, 12 months or longer, Estimated Fair Value	14,531	106,073
Held-to-maturity, 12 months or longer, Unrealized Losses	(150)	(1,693)
Held-to-maturity, Total, Estimated Fair Value	21,839	108,929
Held-to-maturity, Total, Unrealized Losses	(208)	(1,697)
Investment Securities | Corporate Debt Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	9,727	2,470
Held-to-maturity, Less than 12 months, Unrealized Losses	(213)	(21)
Held-to-maturity, 12 months or longer, Estimated Fair Value	37,628	43,059
Held-to-maturity, 12 months or longer, Unrealized Losses	(2,208)	(4,963)
Held-to-maturity, Total, Estimated Fair Value	47,355	45,529
Held-to-maturity, Total, Unrealized Losses	(2,421)	(4,984)
FHLMC | Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	6,329	46,615
Held-to-maturity, Less than 12 months, Unrealized Losses	(29)	(159)
Held-to-maturity, 12 months or longer, Estimated Fair Value	38,641	147,763
Held-to-maturity, 12 months or longer, Unrealized Losses	(495)	(4,951)
Held-to-maturity, Total, Estimated Fair Value	44,970	194,378
Held-to-maturity, Total, Unrealized Losses	(524)	(5,110)
FNMA | Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	13,682	27,594
Held-to-maturity, Less than 12 months, Unrealized Losses	(59)	(125)
Held-to-maturity, 12 months or longer, Estimated Fair Value	38,568	185,328
Held-to-maturity, 12 months or longer, Unrealized Losses	(434)	(5,905)
Held-to-maturity, Total, Estimated Fair Value	52,250	212,922
Held-to-maturity, Total, Unrealized Losses	(493)	(6,030)
GNMA | Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	30,268	35,221
Held-to-maturity, Less than 12 months, Unrealized Losses	(93)	(535)
Held-to-maturity, 12 months or longer, Estimated Fair Value	19,828	59,468
Held-to-maturity, 12 months or longer, Unrealized Losses	(119)	(1,825)
Held-to-maturity, Total, Estimated Fair Value	50,096	94,689
Held-to-maturity, Total, Unrealized Losses	(212)	(2,360)
SBA | Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	0	3,447
Held-to-maturity, Less than 12 months, Unrealized Losses	0	(80)
Held-to-maturity, 12 months or longer, Estimated Fair Value	1,889	0
Held-to-maturity, 12 months or longer, Unrealized Losses	(51)	0
Held-to-maturity, Total, Estimated Fair Value	1,889	3,447
Held-to-maturity, Total, Unrealized Losses	$ (51)	$ (80)