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Investment Securities - Analysis of Amortized Cost and Estimated Fair Values of Securities Available for Sale (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Investment Securities [Line Items] |  |
Amortized Cost | $ 924,054 | $ 740,846
Gross Unrealized Gains | 2,998 | 4,854
Gross Unrealized Losses | (17,805) | (14,342)
Securities available for sale | 909,247 | 731,358
US States and Political Subdivisions Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 27,592 | 27,083
Gross Unrealized Gains | 126 | 327
Gross Unrealized Losses | (6) | 0
Securities available for sale | 27,712 | 27,410
Corporate Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 20,912 | 15,907
Gross Unrealized Gains | 321 | 590
Gross Unrealized Losses | (221) | (4)
Securities available for sale | 21,012 | 16,493
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 0 | 27,499
Gross Unrealized Gains | 0 | 526
Gross Unrealized Losses | 0 | (4,379)
Securities available for sale | 0 | 23,646
Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 924,054 | 739,176
Gross Unrealized Gains | 2,998 | 4,854
Gross Unrealized Losses | (17,805) | (14,342)
Securities available for sale | 909,247 | 729,688
Equity Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 0 | 1,670
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Securities available for sale | 0 | 1,670
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage - Backed Securities - Commercial [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 0 | 0
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage - Backed Securities - Residential [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 686,906 | 632,422
Gross Unrealized Gains | 1,846 | 2,622
Gross Unrealized Losses | (15,391) | (9,489)
Securities available for sale | 673,361 | 625,555
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 10,000 | 1,098
Gross Unrealized Gains | 12 | 0
Gross Unrealized Losses | 0 | (1)
Securities available for sale | 10,012 | 1,097
Obligations of U.S. Government [Member] | Mortgage - Backed Securities - Commercial [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 169,633 | 24,611
Gross Unrealized Gains | 214 | 0
Gross Unrealized Losses | (2,103) | (462)
Securities available for sale | 167,744 | 24,149
Obligations of U.S. Government [Member] | Mortgage - Backed Securities - Residential [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 9,011 | 10,556
Gross Unrealized Gains | 479 | 789
Gross Unrealized Losses | (84) | (7)
Securities available for sale | $ 9,406 | $ 11,338

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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- Definition Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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