Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Securities Financing Transaction [Line Items]
Available-for-sale, Estimated Fair Value	$ 29,902	$ 19,804
Held-to-maturity, Amortized Cost	405,361	481,340
Held-to-maturity, Estimated Fair Value	397,763	474,215
Total, Amortized Cost	435,267	501,240
Total, Gross Unrealized Gains	3,626	5,524
Total, Gross Unrealized Losses	(11,228)	(12,745)
Total, Estimated Fair Value	427,665	494,019
Corporate Debt Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	55,000
Held-to-maturity, Estimated Fair Value	46,473
Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	405,361	481,340
Held-to-maturity, Gross Unrealized Gains	3,603	5,524
Held-to-maturity, Gross Unrealized Losses	(11,201)	(12,649)
Held-to-maturity, Estimated Fair Value	397,763	474,215
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	280,872	326,117
Held-to-maturity, Gross Unrealized Gains	3,498	5,402
Held-to-maturity, Gross Unrealized Losses	(2,612)	(2,841)
Held-to-maturity, Estimated Fair Value	281,758	328,678
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | FHLMC [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	120,116	141,494
Held-to-maturity, Gross Unrealized Gains	364	609
Held-to-maturity, Gross Unrealized Losses	(1,489)	(1,659)
Held-to-maturity, Estimated Fair Value	118,991	140,444
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | FNMA [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	160,254	184,003
Held-to-maturity, Gross Unrealized Gains	3,039	4,674
Held-to-maturity, Gross Unrealized Losses	(1,123)	(1,182)
Held-to-maturity, Estimated Fair Value	162,170	187,495
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | GNMA [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	502	620
Held-to-maturity, Gross Unrealized Gains	95	119
Held-to-maturity, Estimated Fair Value	597	739
Investment Securities [Member] | U.S. Agency Obligations [Member]
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	29,906	19,900
Available-for-sale, Gross Unrealized Gains	23
Available-for-sale, Gross Unrealized Losses	(27)	(96)
Available-for-sale, Estimated Fair Value	29,902	19,804
Investment Securities [Member] | Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	124,489	155,223
Held-to-maturity, Gross Unrealized Gains	105	122
Held-to-maturity, Gross Unrealized Losses	(8,589)	(9,808)
Held-to-maturity, Estimated Fair Value	116,005	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	55,178	86,394
Held-to-maturity, Gross Unrealized Gains	87	97
Held-to-maturity, Gross Unrealized Losses	(59)	(50)
Held-to-maturity, Estimated Fair Value	55,206	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	13,311	13,829
Held-to-maturity, Gross Unrealized Gains	18	25
Held-to-maturity, Gross Unrealized Losses	(3)	(8)
Held-to-maturity, Estimated Fair Value	13,326	13,846
Investment Securities [Member] | Held-to-Maturity Securities [Member] | Corporate Debt Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	56,000	55,000
Held-to-maturity, Gross Unrealized Losses	(8,527)	(9,750)
Held-to-maturity, Estimated Fair Value	$ 47,473	$ 45,250