Securities - Estimated Fair Value and Unrealized Loss for Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Total securities, Less than 12 months, Estimated Fair Value		$ 127,789
Total securities, Less than 12 months, Unrealized Losses		(706)
Total securities, 12 months or longer, Estimated Fair Value		129,057
Total securities, 12 months or longer, Unrealized Losses		(10,522)
Total securities, Estimated Fair Value		256,846
Total securities, Unrealized Losses		(11,228)
Held-to-Maturity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	$ 48,092	112,852
Held-to-maturity, Less than 12 months, Unrealized Losses	(103)	(679)
Held-to-maturity, 12 months or longer, Estimated Fair Value	86,990	129,057
Held-to-maturity, 12 months or longer, Unrealized Losses	(7,490)	(10,522)
Held-to-maturity, Total, Estimated Fair Value	135,082	241,909
Held-to-maturity, Total, Unrealized Losses	(7,593)	(11,201)
Held-to-Maturity Securities [Member] | Investment Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	16,988	33,032
Held-to-maturity, Less than 12 months, Unrealized Losses	(29)	(45)
Held-to-maturity, 12 months or longer, Estimated Fair Value	48,172	52,135
Held-to-maturity, 12 months or longer, Unrealized Losses	(7,106)	(8,544)
Held-to-maturity, Total, Estimated Fair Value	65,160	85,167
Held-to-maturity, Total, Unrealized Losses	(7,135)	(8,589)
Held-to-Maturity Securities [Member] | Investment Securities [Member] | Other investments [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	868
Held-to-maturity, Less than 12 months, Unrealized Losses	(5)
Held-to-maturity, Total, Estimated Fair Value	868
Held-to-maturity, Total, Unrealized Losses	(5)
U.S. Agency Obligations [Member] | Investment Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available-for-sale, Less than 12 months, Estimated Market Value		14,937
Available-for-sale, Less than 12 months, Unrealized Losses		(27)
Available-for-sale, 12 months or longer, Estimated Market Value		0
Available-for-sale, 12 months or longer, Unrealized Losses		0
Available-for-sale, Total, Estimated Market Value		14,937
Available-for-sale, Total, Unrealized Losses		(27)
U.S. Agency Obligations [Member] | Held-to-Maturity Securities [Member] | Investment Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value		30,175
Held-to-maturity, Less than 12 months, Unrealized Losses		(43)
Held-to-maturity, 12 months or longer, Estimated Fair Value		5,023
Held-to-maturity, 12 months or longer, Unrealized Losses		(16)
Held-to-maturity, Total, Estimated Fair Value		35,198
Held-to-maturity, Total, Unrealized Losses		(59)
State and Municipal Obligations [Member] | Held-to-Maturity Securities [Member] | Investment Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	12,117	2,857
Held-to-maturity, Less than 12 months, Unrealized Losses	(22)	(2)
Held-to-maturity, 12 months or longer, Estimated Fair Value	277	639
Held-to-maturity, 12 months or longer, Unrealized Losses	(1)	(1)
Held-to-maturity, Total, Estimated Fair Value	12,394	3,496
Held-to-maturity, Total, Unrealized Losses	(23)	(3)
Corporate Debt Securities [Member] | Held-to-Maturity Securities [Member] | Investment Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	4,003
Held-to-maturity, Less than 12 months, Unrealized Losses	(2)
Held-to-maturity, 12 months or longer, Estimated Fair Value	47,895	46,473
Held-to-maturity, 12 months or longer, Unrealized Losses	(7,105)	(8,527)
Held-to-maturity, Total, Estimated Fair Value	51,898	46,473
Held-to-maturity, Total, Unrealized Losses	(7,107)	(8,527)
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	31,104	79,820
Held-to-maturity, Less than 12 months, Unrealized Losses	(74)	(634)
Held-to-maturity, 12 months or longer, Estimated Fair Value	38,818	76,922
Held-to-maturity, 12 months or longer, Unrealized Losses	(384)	(1,978)
Held-to-maturity, Total, Estimated Fair Value	69,922	156,742
Held-to-maturity, Total, Unrealized Losses	(458)	(2,612)
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member] | FHLMC [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	10,791	35,816
Held-to-maturity, Less than 12 months, Unrealized Losses	(20)	(200)
Held-to-maturity, 12 months or longer, Estimated Fair Value	29,101	53,604
Held-to-maturity, 12 months or longer, Unrealized Losses	(252)	(1,289)
Held-to-maturity, Total, Estimated Fair Value	39,892	89,420
Held-to-maturity, Total, Unrealized Losses	(272)	(1,489)
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member] | FNMA [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	18,847	44,004
Held-to-maturity, Less than 12 months, Unrealized Losses	(47)	(434)
Held-to-maturity, 12 months or longer, Estimated Fair Value	9,717	23,318
Held-to-maturity, 12 months or longer, Unrealized Losses	(132)	(689)
Held-to-maturity, Total, Estimated Fair Value	28,564	67,322
Held-to-maturity, Total, Unrealized Losses	(179)	$ (1,123)
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member] | GNMA [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	1,466
Held-to-maturity, Less than 12 months, Unrealized Losses	(7)
Held-to-maturity, Total, Estimated Fair Value	1,466
Held-to-maturity, Total, Unrealized Losses	$ (7)