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Investment Securities - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items] |  |  |
Maturity of contract | less than one year |  |
Approximate year of maturity | 30 years |  |
Gross Unrealized Gains (Losses) | $ 16,477 | $ 24,420 |
Securities available for sale | 886,560 | 1,309,819 |
Amortized Cost | 891,111 | 1,317,318 |
Gain (loss) on sales of securities | (153) | 550 | $ (1,158)
Available-for-sale securities pledged as collateral | 416,100 | 563,200 |
Held-to-maturity securities pledged as collateral | 45,700 |  |
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Gross Unrealized Gains (Losses) | 500 | $ 1,300 |
Amortized Cost | 6,600 |  |
US Government Agencies Debt Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Sale of available securities | 75,000 |  |
Gain (loss) on sales of securities | $ (300) |  |

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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=28360136&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=6871852&loc=d3e26610-111562 + Details
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- Definition Description of how prepayments are considered in determination of contractual cash flows and cash flows expected to be collected for the loan or debt security. This relates to loans and debt securities for which at acquisition it was probable that the investor would be unable to collect all contractually required payments receivable or all cash flows expected at acquisition. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 15 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15029-111544 + Details
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