Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Securities Financing Transaction [Line Items]
Available-for-sale, Estimated Fair Value	$ 30,085	$ 29,902
Held-to-maturity, Amortized Cost	385,798	405,361
Held-to-maturity, Estimated Fair Value	378,613	397,763
Total, Amortized Cost	415,714	435,267
Total, Gross Unrealized Gains	5,566	3,626
Total, Gross Unrealized Losses	(12,582)	(11,228)
Total, Estimated Fair Value	408,698	427,665
Corporate Debt Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	55,000
Held-to-maturity, Estimated Fair Value	43,091
Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	385,798	405,361
Held-to-maturity, Gross Unrealized Gains	5,397	3,603
Held-to-maturity, Gross Unrealized Losses	(12,582)	(11,201)
Held-to-maturity, Estimated Fair Value	378,613	397,763
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	267,584	280,872
Held-to-maturity, Gross Unrealized Gains	4,963	3,498
Held-to-maturity, Gross Unrealized Losses	(668)	(2,612)
Held-to-maturity, Estimated Fair Value	271,879	281,758
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | FHLMC [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	114,709	120,116
Held-to-maturity, Gross Unrealized Gains	1,011	364
Held-to-maturity, Gross Unrealized Losses	(411)	(1,489)
Held-to-maturity, Estimated Fair Value	115,309	118,991
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | FNMA [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	152,392	160,254
Held-to-maturity, Gross Unrealized Gains	3,854	3,039
Held-to-maturity, Gross Unrealized Losses	(257)	(1,123)
Held-to-maturity, Estimated Fair Value	155,989	162,170
Held-to-Maturity Securities [Member] | Mortgage-Backed Securities [Member] | GNMA [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	483	502
Held-to-maturity, Gross Unrealized Gains	98	95
Held-to-maturity, Estimated Fair Value	581	597
Investment Securities [Member] | U.S. Agency Obligations [Member]
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	29,916	29,906
Available-for-sale, Gross Unrealized Gains	169	23
Available-for-sale, Gross Unrealized Losses		(27)
Available-for-sale, Estimated Fair Value	30,085	29,902
Investment Securities [Member] | Held-to-Maturity Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	118,214	124,489
Held-to-maturity, Gross Unrealized Gains	434	105
Held-to-maturity, Gross Unrealized Losses	(11,914)	(8,589)
Held-to-maturity, Estimated Fair Value	106,734	116,005
Investment Securities [Member] | Held-to-Maturity Securities [Member] | U.S. Agency Obligations [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	50,074	55,178
Held-to-maturity, Gross Unrealized Gains	374	87
Held-to-maturity, Gross Unrealized Losses	(2)	(59)
Held-to-maturity, Estimated Fair Value	50,446	55,206
Investment Securities [Member] | Held-to-Maturity Securities [Member] | State and Municipal Obligations [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	12,140	13,311
Held-to-maturity, Gross Unrealized Gains	60	18
Held-to-maturity, Gross Unrealized Losses	(3)	(3)
Held-to-maturity, Estimated Fair Value	12,197	13,326
Investment Securities [Member] | Held-to-Maturity Securities [Member] | Corporate Debt Securities [Member]
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	56,000	56,000
Held-to-maturity, Gross Unrealized Losses	(11,909)	(8,527)
Held-to-maturity, Estimated Fair Value	$ 44,091	$ 47,473