FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets measured at Fair Value
Available-for-sale securities	$ 1,251,451	$ 1,146,317
Mortgage-backed
Assets measured at Fair Value
Available-for-sale securities	267,650	248,986
ABS/CMO
Assets measured at Fair Value
Available-for-sale securities	74,396	56,953
Non-U.S. govt. & agency
Assets measured at Fair Value
Available-for-sale securities	8,698	6,697
U.S. Government
Assets measured at Fair Value
Available-for-sale securities	16,074	16,172
U.S. Agencies
Assets measured at Fair Value
Available-for-sale securities	73,431	113,819
States, political subdivisions, and revenues
Assets measured at Fair Value
Available-for-sale securities	290,802	236,590
Fair value measured on recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets measured at Fair Value
Available-for-sale securities	406,399	388,689
Total assets at fair value	406,399	388,689
Fair value measured on recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Equities
Assets measured at Fair Value
Available-for-sale securities	406,399	388,689
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Trading securities	8	7
Available-for-sale securities	1,251,451	1,146,317
Total assets at fair value	1,251,459	1,146,324
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| Mortgage-backed
Assets measured at Fair Value
Trading securities		7
Available-for-sale securities	267,650	248,986
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| ABS/CMO
Assets measured at Fair Value
Trading securities	8
Available-for-sale securities	74,396	56,953
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| Non-U.S. govt. & agency
Assets measured at Fair Value
Available-for-sale securities	8,698	6,697
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| U.S. Government
Assets measured at Fair Value
Available-for-sale securities	16,074	16,172
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| U.S. Agencies
Assets measured at Fair Value
Available-for-sale securities	73,431	113,819
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| Corporates
Assets measured at Fair Value
Available-for-sale securities	520,400	467,100
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| States, political subdivisions, and revenues
Assets measured at Fair Value
Available-for-sale securities	290,802	236,590
Fair value measured on recurring basis \| Total
Assets measured at Fair Value
Trading securities	8	7
Available-for-sale securities	1,657,850	1,535,006
Total assets at fair value	1,657,858	1,535,013
Fair value measured on recurring basis \| Total \| Mortgage-backed
Assets measured at Fair Value
Trading securities		7
Available-for-sale securities	267,650	248,986
Fair value measured on recurring basis \| Total \| ABS/CMO
Assets measured at Fair Value
Trading securities	8
Available-for-sale securities	74,396	56,953
Fair value measured on recurring basis \| Total \| Non-U.S. govt. & agency
Assets measured at Fair Value
Available-for-sale securities	8,698	6,697
Fair value measured on recurring basis \| Total \| U.S. Government
Assets measured at Fair Value
Available-for-sale securities	16,074	16,172
Fair value measured on recurring basis \| Total \| U.S. Agencies
Assets measured at Fair Value
Available-for-sale securities	73,431	113,819
Fair value measured on recurring basis \| Total \| Corporates
Assets measured at Fair Value
Available-for-sale securities	520,400	467,100
Fair value measured on recurring basis \| Total \| States, political subdivisions, and revenues
Assets measured at Fair Value
Available-for-sale securities	290,802	236,590
Fair value measured on recurring basis \| Total \| Equities
Assets measured at Fair Value
Available-for-sale securities	$ 406,399	$ 388,689

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

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