Securities - Estimated Fair Value and Unrealized Loss of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Total securities, Less than 12 months, Estimated Fair Value	$ 4,453	$ 45,040
Total securities, Less than 12 months, Unrealized Losses	(12)	(140)
Total securities, 12 months or longer, Estimated Fair Value	135,616	234,393
Total securities, 12 months or longer, Unrealized Losses	(8,055)	(12,605)
Total securities, Estimated Fair Value	140,069	279,433
Total securities, Unrealized Losses	(8,067)	(12,745)
Investment Securities [Member] | U.S. Agency Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available-for-sale, Less than 12 months, Estimated Market Value		19,804
Available-for-sale, Less than 12 months, Unrealized Losses		(96)
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		19,804
Available-for-sale, Total, Unrealized Losses		(96)
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	4,453	25,236
Held-to-maturity, Less than 12 months, Unrealized Losses	(12)	(44)
Held-to-maturity, 12 months or longer, Estimated Fair Value	135,616	234,393
Held-to-maturity, 12 months or longer, Unrealized Losses	(8,055)	(12,605)
Held-to-maturity, Total, Estimated Fair Value	140,069	259,629
Held-to-maturity, Total, Unrealized Losses	(8,067)	(12,649)
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	852	16,081
Held-to-maturity, Less than 12 months, Unrealized Losses	(2)	(10)
Held-to-maturity, 12 months or longer, Estimated Fair Value	53,763	72,486
Held-to-maturity, 12 months or longer, Unrealized Losses	(6,931)	(9,798)
Held-to-maturity, Total, Estimated Fair Value	54,615	88,567
Held-to-maturity, Total, Unrealized Losses	(6,933)	(9,808)
Held-to-Maturity Securities [Member] | Investment Securities [Member] | U.S. Agency Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value		15,134
Held-to-maturity, Less than 12 months, Unrealized Losses		(9)
Held-to-maturity, 12 months or longer, Estimated Fair Value	5,048	25,409
Held-to-maturity, 12 months or longer, Unrealized Losses	(2)	(41)
Held-to-maturity, Total, Estimated Fair Value	5,048	40,543
Held-to-maturity, Total, Unrealized Losses	(2)	(50)
Held-to-Maturity Securities [Member] | Investment Securities [Member] | State and Municipal Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, Less than 12 months, Estimated Fair Value	852	947
Held-to-maturity, Less than 12 months, Unrealized Losses	(2)	(1)
Held-to-maturity, 12 months or longer, Estimated Fair Value	643	1,827
Held-to-maturity, 12 months or longer, Unrealized Losses	(1)	(7)
Held-to-maturity, Total, Estimated Fair Value	1,495	2,774
Held-to-maturity, Total, Unrealized Losses	(3)	(8)
Held-to-Maturity Securities [Member] | Investment Securities [Member] | Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, 12 months or longer, Estimated Fair Value	48,072	45,250
Held-to-maturity, 12 months or longer, Unrealized Losses	(6,928)	(9,750)
Held-to-maturity, Total, Estimated Fair Value	48,072	45,250
Held-to-maturity, Total, Unrealized Losses	(6,928)	(9,750)
Held-to-Maturity Securities [Member] | Mortgage-Backed 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	3,601	9,155
Held-to-maturity, Less than 12 months, Unrealized Losses	(10)	(34)
Held-to-maturity, 12 months or longer, Estimated Fair Value	81,853	161,907
Held-to-maturity, 12 months or longer, Unrealized Losses	(1,124)	(2,807)
Held-to-maturity, Total, Estimated Fair Value	85,454	171,062
Held-to-maturity, Total, Unrealized Losses	(1,134)	(2,841)
Held-to-Maturity Securities [Member] | Mortgage-Backed 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	3,601	9,155
Held-to-maturity, Less than 12 months, Unrealized Losses	(10)	(34)
Held-to-maturity, 12 months or longer, Estimated Fair Value	57,076	96,975
Held-to-maturity, 12 months or longer, Unrealized Losses	(648)	(1,625)
Held-to-maturity, Total, Estimated Fair Value	60,677	106,130
Held-to-maturity, Total, Unrealized Losses	(658)	(1,659)
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | FNMA [Member]
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Held-to-maturity, 12 months or longer, Estimated Fair Value	24,777	64,932
Held-to-maturity, 12 months or longer, Unrealized Losses	(476)	(1,182)
Held-to-maturity, Total, Estimated Fair Value	24,777	64,932
Held-to-maturity, Total, Unrealized Losses	$ (476)	$ (1,182)