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Investments - Investment Securities Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2014 | Dec. 31, 2013
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Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | $ 87,871 | $ 68,985
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss | 239 | 1,188
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,746 | 2,227
Held-to-maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer, Accumulated Loss | 85 | 150
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 89,617 | 71,212
Held-to-maturity Securities, Gross Unrealized Losses | 324 | 1,338
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 87,150 | 138,107
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 499 | 6,191
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater | 18,165 | 7,525
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater | 3,595 | 2,844
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 105,315 | 145,632
Available-for Sale, Gross Unrealized Losses, Total | 4,094 | 9,035
Fair Value of Investments with Unrealized Losses, Less Than 12 months | 175,021 | 207,092
Gross Unrealized Loss, Less Than 12 Months | 738 | 7,379
Fair Value of Investments with Unrealized Losses, 12 Months or Greater | 19,911 | 9,752
Gross Unrealized Losses, 12 Months or Greater | 3,680 | 2,994
Fair Value of Investments with Unrealized Losses, Total | 194,932 | 216,844
Gross Unrealized Losses, Total | 4,418 | 10,373
Corporate Bonds [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 77,260 | 14,090
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss | 204 | 41
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 77,260 | 14,090
Held-to-maturity Securities, Gross Unrealized Losses | 204 | 41
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 78,350 | 29,691
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 314 | 361
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater |  |
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater |  |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 78,350 | 29,691
Available-for Sale, Gross Unrealized Losses, Total | 314 | 361
States and Political Subdivisions [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 7,760 | 54,895
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss | 34 | 1,147
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 311
Held-to-maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer, Accumulated Loss |  | 6
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 7,760 | 55,206
Held-to-maturity Securities, Gross Unrealized Losses | 34 | 1,153
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 6,894 | 101,908
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 33 | 4,798
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater | 11,070 | 1,753
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater | 1,566 | 342
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 17,964 | 103,661
Available-for Sale, Gross Unrealized Losses, Total | 1,599 | 5,140
U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 724 | 1,303
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 60 | 465
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater | 7,095 | 5,772
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater | 2,029 | 2,502
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 7,819 | 7,075
Available-for Sale, Gross Unrealized Losses, Total | 2,089 | 2,967
Equity securities [Member] |  |
Investment [Line Items] |  |
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months | 1,182 | 5,205
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months | 92 | 567
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater |  |
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater |  |
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total | 1,182 | 5,205
Available-for Sale, Gross Unrealized Losses, Total | 92 | 567
Asset-Backed Securities [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,746 | 1,916
Held-to-maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer, Accumulated Loss | 85 | 144
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 1,746 | 1,916
Held-to-maturity Securities, Gross Unrealized Losses | 85 | 144
U.S. Treasury securities and obligations of U.S. Government agencies [Member] |  |
Investment [Line Items] |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 2,851 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss | 1 |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value | 2,851 |
Held-to-maturity Securities, Gross Unrealized Losses | $ 1 |

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