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Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities Available for Sale (Detail) (1) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015
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Investment Securities [Line Items] |  |
Amortized Cost | $ 805,116 | $ 891,111
Securities available for sale, at fair value | 813,659 | 886,560
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 17,187 | 11,926
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax | 8,644 | 16,477
Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 19,300 | 19,201
Securities available for sale, at fair value | 19,307 | 19,118
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 7 | 2
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax | 0 | 85
US Government Agencies Residential Mortgage-backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 16,059 |
Securities available for sale, at fair value | 17,976 | $ 22,092
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 692,100 |
Securities available for sale, at fair value | 704,600 |
Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 803,446 |
Securities available for sale, at fair value | $ 811,989 |

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- Definition Investment Securities [Line Items] + References No definition available. + Details
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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + 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=27724398&loc=d3e27161-111563 + Details
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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale. + 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 (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + 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=51813488&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=27724398&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=49167202&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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