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Investment Securities - Analysis of Amortized Cost and Estimated Fair Values of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2014 | Mar. 31, 2012 | Dec. 31, 2013
Investment Securities [Line Items] |  |  |
Amortized Cost | $ 1,370,681 |  | $ 1,350,466
Gross Unrealized Gains | 16,068 | 15,565 |
Gross Unrealized Losses | (35,710) | (47,666) |
Securities available for sale, at fair value | (1,351,039) |  | (1,318,365)
US Government Agencies Residential Mortgage-backed Securities [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 21,648 |  | 22,639
Gross Unrealized Gains | 2,627 | 2,624 |
Gross Unrealized Losses | 34 | (59) |
Securities available for sale, at fair value | (24,241) |  | (25,204)
Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Residential [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 1,020,102 |  | 1,009,519
Gross Unrealized Gains | 12,977 | 12,531 |
Gross Unrealized Losses | 19,472 | (27,163) |
Securities available for sale, at fair value | (1,013,607) |  | (994,887)
Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Commercial [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 96 |  | 104
Gross Unrealized Gains | 2 | 1 |
Gross Unrealized Losses | 0 | 0 |
Securities available for sale, at fair value | (98) |  | (105)
Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 269,170 |  | 267,971
Gross Unrealized Gains | 3 | 81 |
Gross Unrealized Losses | 1,863 | (1,927) |
Securities available for sale, at fair value | (267,310) |  | (266,125)
Obligations of States and Political Subdivisions [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 9,340 |  | 80
Gross Unrealized Gains | 22 | 0 |
Gross Unrealized Losses | 3 | 0 |
Securities available for sale, at fair value | (9,359) |  | (80)
Corporate Debt Securities [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 6,691 |  | 6,693
Gross Unrealized Gains | 437 | 328 |
Gross Unrealized Losses | 0 | 0 |
Securities available for sale, at fair value | (7,128) |  | (7,021)
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 42,214 |  | 42,040
Gross Unrealized Gains | 0 | 0 |
Gross Unrealized Losses | (14,338) | (18,517) |
Securities available for sale, at fair value | (27,876) |  | (23,523)
Debt Securities [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 1,369,261 |  | 1,349,046
Gross Unrealized Gains | 16,068 | 15,565 |
Gross Unrealized Losses | (35,710) | (47,666) |
Securities available for sale, at fair value | (1,349,619) |  | (1,316,945)
Equity Securities [Member] |  |  |
Investment Securities [Line Items] |  |  |
Amortized Cost | 1,420 |  | 1,420
Gross Unrealized Gains | 0 | 0 |
Gross Unrealized Losses | 0 | 0 |
Securities available for sale, at fair value | $ (1,420) |  | $ (1,420)

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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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- Definition Amount of unrealized loss before deducting unrealized gain on investments in 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 (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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