Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Securities Financing Transaction [Line Items]
Available-for-sale, Estimated Fair Value	$ 47,104	$ 12,224
Held-to-maturity, Amortized Cost	704,767	607,833
Held-to-maturity, Estimated Fair Value	695,564	598,119
Total, Amortized Cost	752,079	620,375
Total, Gross Unrealized Gains	2,833	2,681
Total, Gross Unrealized Losses	(12,244)	(12,748)
Total, Estimated Fair Value	742,668	610,308
Held-to-Maturity Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	704,767	607,833
Held-to-maturity, Gross Unrealized Gains	2,752	2,681
Held-to-maturity, Gross Unrealized Losses	(11,955)	(12,430)
Held-to-maturity, Estimated Fair Value	695,564	598,084
Held-to-Maturity Securities | Investment Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	185,824	144,950
Held-to-maturity, Gross Unrealized Gains	409	164
Held-to-maturity, Gross Unrealized Losses	(6,760)	(7,085)
Held-to-maturity, Estimated Fair Value	179,473	138,029
Held-to-Maturity Securities | Other investments | Investment Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	8,820	8,778
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized Losses	(232)	(228)
Held-to-maturity, Estimated Fair Value	8,588	8,550
U.S. Agency Obligations | Held-to-Maturity Securities | Investment Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	19,962	19,960
Held-to-maturity, Gross Unrealized Gains	70	69
Held-to-maturity, Gross Unrealized Losses		(856)
Held-to-maturity, Estimated Fair Value	20,032	20,029
State and Municipal Obligations | Held-to-Maturity Securities | Investment Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	80,993	39,155
Held-to-maturity, Gross Unrealized Gains	121	10
Held-to-maturity, Gross Unrealized Losses	(564)	(856)
Held-to-maturity, Estimated Fair Value	80,550	38,309
Corporate Debt Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	55,000
Held-to-maturity, Estimated Fair Value	49,118
Corporate Debt Securities | Held-to-Maturity Securities | Investment Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	76,049	77,057
Held-to-maturity, Gross Unrealized Gains	218	85
Held-to-maturity, Gross Unrealized Losses	(5,964)	(6,001)
Held-to-maturity, Estimated Fair Value	70,303	71,141
Mortgage-Backed Securities | Held-to-Maturity Securities
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	518,943	462,883
Held-to-maturity, Gross Unrealized Gains	2,343	2,517
Held-to-maturity, Gross Unrealized Losses	(5,195)	(5,345)
Held-to-maturity, Estimated Fair Value	516,091	460,055
Mortgage-Backed Securities | Held-to-Maturity Securities | FHLMC
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	181,310	144,016
Held-to-maturity, Gross Unrealized Gains	246	195
Held-to-maturity, Gross Unrealized Losses	(2,301)	(2,457)
Held-to-maturity, Estimated Fair Value	179,255	141,754
Mortgage-Backed Securities | Held-to-Maturity Securities | FNMA
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	241,800	217,445
Held-to-maturity, Gross Unrealized Gains	1,982	2,175
Held-to-maturity, Gross Unrealized Losses	(2,283)	(2,524)
Held-to-maturity, Estimated Fair Value	241,499	217,096
Mortgage-Backed Securities | Held-to-Maturity Securities | GNMA
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	87,301	92,475
Held-to-maturity, Gross Unrealized Gains	88	119
Held-to-maturity, Gross Unrealized Losses	(611)	(364)
Held-to-maturity, Estimated Fair Value	86,778	92,230
Mortgage-Backed Securities | Held-to-Maturity Securities | SBA
Securities Financing Transaction [Line Items]
Held-to-maturity, Amortized Cost	8,532	8,947
Held-to-maturity, Gross Unrealized Gains	27	28
Held-to-maturity, Estimated Fair Value	8,559	8,975
Investment Securities | U.S. Agency Obligations
Securities Financing Transaction [Line Items]
Available-for-sale, Amortized Cost	47,312	12,542
Available-for-sale, Gross Unrealized Gains	81	0
Available-for-sale, Gross Unrealized Losses	(289)	(318)
Available-for-sale, Estimated Fair Value	$ 47,104	$ 12,224