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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, 2015 | Dec. 31, 2014
Investment Securities [Line Items] |  |
Amortized Cost | $ 891,111 | $ 1,317,318
Gross Unrealized Gains | 11,926 | 16,921
Gross Unrealized Losses | (16,477) | (24,420)
Estimated Fair Value of Available for Sale | 886,560 | 1,309,819
US States and Political Subdivisions Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 27,066 | 27,058
Gross Unrealized Gains | 532 | 362
Gross Unrealized Losses | 0 | (43)
Estimated Fair Value of Available for Sale | 27,598 | 27,377
Corporate Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 1,897 | 6,682
Gross Unrealized Gains | 422 | 573
Gross Unrealized Losses | 0 | 0
Estimated Fair Value of Available for Sale | 2,319 | 7,255
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 42,239 | 41,926
Gross Unrealized Gains | 916 | 309
Gross Unrealized Losses | (7,497) | (13,236)
Estimated Fair Value of Available for Sale | 35,658 | 28,999
Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 888,941 | 1,315,898
Gross Unrealized Gains | 11,926 | 16,921
Gross Unrealized Losses | (16,477) | (24,420)
Estimated Fair Value of Available for Sale | 884,390 | 1,308,399
Mortgage - Backed Securities - Residential [Member] | US Government Agencies Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 20,034 | 23,344
Gross Unrealized Gains | 2,071 | 2,595
Gross Unrealized Losses | (13) | (3)
Estimated Fair Value of Available for Sale | 22,092 | 25,936
Mortgage - Backed Securities - Residential [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 778,476 | 947,635
Gross Unrealized Gains | 7,983 | 13,076
Gross Unrealized Losses | (8,882) | (9,830)
Estimated Fair Value of Available for Sale | 777,577 | 950,881
Mortgage - Backed Securities - Commercial [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 28 | 72
Gross Unrealized Gains | 0 | 2
Gross Unrealized Losses | 0 | 0
Estimated Fair Value of Available for Sale | 28 | 74
Other Government - Sponsored Enterprises [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 19,201 | 269,181
Gross Unrealized Gains | 2 | 4
Gross Unrealized Losses | (85) | (1,308)
Estimated Fair Value of Available for Sale | 19,118 | 267,877
Equity Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 2,170 | 1,420
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Estimated Fair Value of Available for Sale | $ 2,170 | $ 1,420

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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=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 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=27724398&loc=d3e27161-111563 + Details
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