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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, 2016 | Dec. 31, 2015
Investment Securities [Line Items] |  |
Amortized Cost | $ 790,082 | $ 891,111
Gross Unrealized Gains | 7,076 | 11,926
Gross Unrealized Losses | (18,546) | (16,477)
Estimated Fair Value of Available for Sale | 778,612 | 886,560
US States and Political Subdivisions Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 27,075 | 27,066
Gross Unrealized Gains | 195 | 532
Gross Unrealized Losses | (41) | 0
Estimated Fair Value of Available for Sale | 27,229 | 27,598
Corporate Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 5,903 | 1,897
Gross Unrealized Gains | 416 | 422
Gross Unrealized Losses | 0 | 0
Estimated Fair Value of Available for Sale | 6,319 | 2,319
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 39,989 | 42,239
Gross Unrealized Gains | 427 | 916
Gross Unrealized Losses | (7,124) | (7,497)
Estimated Fair Value of Available for Sale | 33,292 | 35,658
Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 788,412 | 888,941
Gross Unrealized Gains | 7,076 | 11,926
Gross Unrealized Losses | (18,546) | (16,477)
Estimated Fair Value of Available for Sale | 776,942 | 884,390
Mortgage - Backed Securities - Residential [Member] | US Government Agencies Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 15,143 | 20,034
Gross Unrealized Gains | 1,481 | 2,071
Gross Unrealized Losses | (7) | (13)
Estimated Fair Value of Available for Sale | 16,617 | 22,092
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 683,601 | 778,476
Gross Unrealized Gains | 4,557 | 7,983
Gross Unrealized Losses | (11,305) | (8,882)
Estimated Fair Value of Available for Sale | 676,853 | 777,577
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 1 | 28
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Estimated Fair Value of Available for Sale | 1 | 28
Other Government - Sponsored Enterprises [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 16,700 | 19,201
Gross Unrealized Gains | 0 | 2
Gross Unrealized Losses | (69) | (85)
Estimated Fair Value of Available for Sale | 16,631 | 19,118
Equity Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 1,670 | 2,170
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Estimated Fair Value of Available for Sale | $ 1,670 | $ 2,170

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- Definition Investment Securities [Line Items] + References No definition available. + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562 + 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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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