Securities - Schedule of Fair Value and Amortized Cost of Available-for-sale and Held-to-maturity Debt Securities (Detail) - USD ($)
$ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
$ 1,766,288
|
$ 1,280,585
|
| Available-for-sale, Gross Unrealized Gains |
2,497
|
3,397
|
| Available-for-sale, Gross Unrealized Losses |
(40,408)
|
(22,117)
|
| Available-for-sale, Estimated Fair Value |
1,728,377
|
1,261,865
|
| Held-to-maturity, Amortized Cost |
1,006,042
|
1,009,500
|
| Held-to-maturity, Gross Unrealized Gains |
10,893
|
18,827
|
| Held-to-maturity, Gross Unrealized Losses |
(11,433)
|
(4,543)
|
| Held-to-maturity securities, Fair value |
1,005,502
|
1,023,784
|
| Total securities, Amortized Cost |
2,772,330
|
2,290,085
|
| Total securities, Gross Unrealized Gains |
13,390
|
22,224
|
| Total securities, Gross Unrealized Losses |
(51,841)
|
(26,660)
|
| Total securities, Estimated Fair Value |
2,733,879
|
2,285,649
|
| US Treasury Securities [Member] |
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
9,900
|
|
| Available-for-sale, Gross Unrealized Losses |
(6)
|
|
| Available-for-sale, Estimated Fair Value |
9,894
|
|
| U.S. Government Sponsored Entities and Agencies [Member] |
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
98,166
|
72,425
|
| Available-for-sale, Gross Unrealized Gains |
1
|
24
|
| Available-for-sale, Gross Unrealized Losses |
(1,709)
|
(606)
|
| Available-for-sale, Estimated Fair Value |
96,458
|
71,843
|
| Held-to-maturity, Amortized Cost |
11,263
|
11,465
|
| Held-to-maturity, Gross Unrealized Losses |
(373)
|
(325)
|
| Held-to-maturity securities, Fair value |
10,890
|
11,140
|
| Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member] |
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
1,377,904
|
954,115
|
| Available-for-sale, Gross Unrealized Gains |
214
|
214
|
| Available-for-sale, Gross Unrealized Losses |
(33,708)
|
(19,407)
|
| Available-for-sale, Estimated Fair Value |
1,344,410
|
934,922
|
| Held-to-maturity, Amortized Cost |
162,904
|
170,025
|
| Held-to-maturity, Gross Unrealized Gains |
301
|
544
|
| Held-to-maturity, Gross Unrealized Losses |
(4,987)
|
(2,609)
|
| Held-to-maturity securities, Fair value |
158,218
|
167,960
|
| Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member] |
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
144,568
|
116,448
|
| Available-for-sale, Gross Unrealized Gains |
19
|
4
|
| Available-for-sale, Gross Unrealized Losses |
(3,661)
|
(1,585)
|
| Available-for-sale, Estimated Fair Value |
140,926
|
114,867
|
| Obligations of State and Political Subdivisions [Member] |
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
100,531
|
102,363
|
| Available-for-sale, Gross Unrealized Gains |
2,093
|
2,927
|
| Available-for-sale, Gross Unrealized Losses |
(1,193)
|
(460)
|
| Available-for-sale, Estimated Fair Value |
101,431
|
104,830
|
| Held-to-maturity, Amortized Cost |
798,536
|
794,655
|
| Held-to-maturity, Gross Unrealized Gains |
10,510
|
17,364
|
| Held-to-maturity, Gross Unrealized Losses |
(5,838)
|
(1,609)
|
| Held-to-maturity securities, Fair value |
803,208
|
810,410
|
| Corporate Debt Securities [Member] |
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available-for-sale, Amortized Cost |
35,219
|
35,234
|
| Available-for-sale, Gross Unrealized Gains |
170
|
228
|
| Available-for-sale, Gross Unrealized Losses |
(131)
|
(59)
|
| Available-for-sale, Estimated Fair Value |
35,258
|
35,403
|
| Held-to-maturity, Amortized Cost |
33,339
|
33,355
|
| Held-to-maturity, Gross Unrealized Gains |
82
|
919
|
| Held-to-maturity, Gross Unrealized Losses |
(235)
|
|
| Held-to-maturity securities, Fair value |
$ 33,186
|
$ 34,274
|