Securities - Estimated Fair Value and Unrealized Loss for Securities Available-for-Sale and Held-to-Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Total securities, Less than 12 months, Estimated Fair Value	$ 45,040
Total securities, Less than 12 months, Unrealized Losses	(140)
Total securities, 12 months or longer, Estimated Fair Value	234,393
Total securities, 12 months or longer, Unrealized Losses	(12,605)
Total securities, Estimated Fair Value	279,433
Total securities, Unrealized Losses	(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	25,236	246,105
Held-to-maturity, Less than 12 months, Unrealized Losses	(44)	(8,334)
Held-to-maturity, 12 months or longer, Estimated Fair Value	234,393	45,403
Held-to-maturity, 12 months or longer, Unrealized Losses	(12,605)	(10,754)
Held-to-maturity, Total, Estimated Fair Value	259,629	291,508
Held-to-maturity, Total, Unrealized Losses	(12,649)	(19,088)
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	16,081	39,273
Held-to-maturity, Less than 12 months, Unrealized Losses	(10)	(175)
Held-to-maturity, 12 months or longer, Estimated Fair Value	72,486	45,403
Held-to-maturity, 12 months or longer, Unrealized Losses	(9,798)	(10,754)
Held-to-maturity, Total, Estimated Fair Value	88,567	84,676
Held-to-maturity, Total, Unrealized Losses	(9,808)	(10,929)
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	35,747
Held-to-maturity, Less than 12 months, Unrealized Losses	(9)	(144)
Held-to-maturity, 12 months or longer, Estimated Fair Value	25,409
Held-to-maturity, 12 months or longer, Unrealized Losses	(41)
Held-to-maturity, Total, Estimated Fair Value	40,543	35,747
Held-to-maturity, Total, Unrealized Losses	(50)	(144)
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	947	3,526
Held-to-maturity, Less than 12 months, Unrealized Losses	(1)	(31)
Held-to-maturity, 12 months or longer, Estimated Fair Value	1,827	1,153
Held-to-maturity, 12 months or longer, Unrealized Losses	(7)	(4)
Held-to-maturity, Total, Estimated Fair Value	2,774	4,679
Held-to-maturity, Total, Unrealized Losses	(8)	(35)
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	45,250	44,250
Held-to-maturity, 12 months or longer, Unrealized Losses	(9,750)	(10,750)
Held-to-maturity, Total, Estimated Fair Value	45,250	44,250
Held-to-maturity, Total, Unrealized Losses	(9,750)	(10,750)
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	9,155	206,832
Held-to-maturity, Less than 12 months, Unrealized Losses	(34)	(8,159)
Held-to-maturity, 12 months or longer, Estimated Fair Value	161,907
Held-to-maturity, 12 months or longer, Unrealized Losses	(2,807)
Held-to-maturity, Total, Estimated Fair Value	171,062	206,832
Held-to-maturity, Total, Unrealized Losses	(2,841)	(8,159)
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	9,155	122,365
Held-to-maturity, Less than 12 months, Unrealized Losses	(34)	(4,552)
Held-to-maturity, 12 months or longer, Estimated Fair Value	96,975
Held-to-maturity, 12 months or longer, Unrealized Losses	(1,625)
Held-to-maturity, Total, Estimated Fair Value	106,130	122,365
Held-to-maturity, Total, Unrealized Losses	(1,659)	(4,552)
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, Less than 12 months, Estimated Fair Value		84,467
Held-to-maturity, Less than 12 months, Unrealized Losses		(3,607)
Held-to-maturity, 12 months or longer, Estimated Fair Value	64,932
Held-to-maturity, 12 months or longer, Unrealized Losses	(1,182)
Held-to-maturity, Total, Estimated Fair Value	64,932	84,467
Held-to-maturity, Total, Unrealized Losses	$ (1,182)	$ (3,607)