Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Securities Financing Transaction [Line Items]
Available-for-sale, Estimated Fair Value	$ 30,030	$ 19,804
Held-to-maturity, Amortized Cost	425,904	481,340
Held-to-maturity, Estimated Fair Value	420,409	474,215
Total, Amortized Cost	455,791	501,240
Total, Gross Unrealized Gains	4,620	5,524
Total, Gross Unrealized Losses	(9,972)	(12,745)
Total, Estimated Fair Value	450,439	494,019
Corporate Debt Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	55,000
Held-to-maturity, Estimated Fair Value	47,250
Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	425,904	481,340
Held-to-maturity, Gross Unrealized Gains	4,477	5,524
Held-to-maturity, Gross Unrealized Losses	(9,972)	(12,649)
Held-to-maturity, Estimated Fair Value	420,409	474,215
Investment Securities [Member] | U.S. Agency Obligations [Member]
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	29,887	19,900
Available-for-sale, Gross Unrealized Gains	143
Available-for-sale, Gross Unrealized Losses		(96)
Available-for-sale, Estimated Fair Value	30,030	19,804
Investment Securities [Member] | Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	131,434	155,223
Held-to-maturity, Gross Unrealized Gains	150	122
Held-to-maturity, Gross Unrealized Losses	(7,761)	(9,808)
Held-to-maturity, Estimated Fair Value	123,823	145,537
Investment Securities [Member] | Held-to-Maturity Securities [Member] | U.S. Agency Obligations [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	65,467	86,394
Held-to-maturity, Gross Unrealized Gains	135	97
Held-to-maturity, Gross Unrealized Losses	(2)	(50)
Held-to-maturity, Estimated Fair Value	65,600	86,441
Investment Securities [Member] | Held-to-Maturity Securities [Member] | State and Municipal Obligations [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	10,967	13,829
Held-to-maturity, Gross Unrealized Gains	15	25
Held-to-maturity, Gross Unrealized Losses	(9)	(8)
Held-to-maturity, Estimated Fair Value	10,973	13,846
Investment Securities [Member] | Held-to-Maturity Securities [Member] | Corporate Debt Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	55,000	55,000
Held-to-maturity, Gross Unrealized Losses	(7,750)	(9,750)
Held-to-maturity, Estimated Fair Value	47,250	45,250
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	294,470	326,117
Held-to-maturity, Gross Unrealized Gains	4,327	5,402
Held-to-maturity, Gross Unrealized Losses	(2,211)	(2,841)
Held-to-maturity, Estimated Fair Value	296,586	328,678
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member] | FHLMC [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	128,701	141,494
Held-to-maturity, Gross Unrealized Gains	565	609
Held-to-maturity, Gross Unrealized Losses	(1,280)	(1,659)
Held-to-maturity, Estimated Fair Value	127,986	140,444
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member] | FNMA [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	165,220	184,003
Held-to-maturity, Gross Unrealized Gains	3,669	4,674
Held-to-maturity, Gross Unrealized Losses	(931)	(1,182)
Held-to-maturity, Estimated Fair Value	167,958	187,495
Mortgage-Backed Securities [Member] | Held-to-Maturity Securities [Member] | GNMA [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	549	620
Held-to-maturity, Gross Unrealized Gains	93	119
Held-to-maturity, Estimated Fair Value	$ 642	$ 739