FAIR VALUE MEASUREMENTS (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Assets measured at Fair Value
Available-for-sale securities	$ 1,399,510,000	$ 1,378,582,000
Transfers in (out of) level 1	0
Transfers in (out of) level 2	0
Mortgage-backed
Assets measured at Fair Value
Available-for-sale securities	263,455,000	250,387,000
ABS/CMBS
Assets measured at Fair Value
Available-for-sale securities	93,421,000	77,329,000
Non-U.S. govt. & agency
Assets measured at Fair Value
Available-for-sale securities	8,849,000	9,367,000
U.S. government
Assets measured at Fair Value
Available-for-sale securities	17,255,000	16,713,000
U.S. agency
Assets measured at Fair Value
Available-for-sale securities	8,588,000	11,759,000
Equity
Assets measured at Fair Value
Available-for-sale securities	416,814,000	375,788,000
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	416,814,000	375,788,000
Total assets at fair value	416,814,000	375,788,000
Fair value measured on recurring basis \| Quoted Prices in Active Markets for Identical Assets (Level 1) \| Equity
Assets measured at Fair Value
Available-for-sale securities	416,814,000	375,788,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2)
Assets measured at Fair Value
Trading securities		7,000
Available-for-sale securities	1,399,510,000	1,378,582,000
Total assets at fair value	1,399,510,000	1,378,589,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| Corporate
Assets measured at Fair Value
Available-for-sale securities	509,751,000	580,708,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| Mortgage-backed
Assets measured at Fair Value
Trading securities		7,000
Available-for-sale securities	263,455,000	250,387,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| ABS/CMBS
Assets measured at Fair Value
Available-for-sale securities	93,421,000	77,329,000
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	8,849,000	9,367,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| U.S. government
Assets measured at Fair Value
Available-for-sale securities	17,255,000	16,713,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| U.S. agency
Assets measured at Fair Value
Available-for-sale securities	8,588,000	11,759,000
Fair value measured on recurring basis \| Significant Other Observable Inputs (Level 2) \| Municipal
Assets measured at Fair Value
Available-for-sale securities	498,191,000	432,319,000
Fair value measured on recurring basis \| Significant Unobservable Inputs (Level 3)
Assets measured at Fair Value
Total assets at fair value	0
Fair value measured on recurring basis \| Total
Assets measured at Fair Value
Trading securities		7,000
Available-for-sale securities	1,816,324,000	1,754,370,000
Total assets at fair value	1,816,324,000	1,754,377,000
Fair value measured on recurring basis \| Total \| Corporate
Assets measured at Fair Value
Available-for-sale securities	509,751,000	580,708,000
Fair value measured on recurring basis \| Total \| Mortgage-backed
Assets measured at Fair Value
Trading securities		7,000
Available-for-sale securities	263,455,000	250,387,000
Fair value measured on recurring basis \| Total \| ABS/CMBS
Assets measured at Fair Value
Available-for-sale securities	93,421,000	77,329,000
Fair value measured on recurring basis \| Total \| Non-U.S. govt. & agency
Assets measured at Fair Value
Available-for-sale securities	8,849,000	9,367,000
Fair value measured on recurring basis \| Total \| U.S. government
Assets measured at Fair Value
Available-for-sale securities	17,255,000	16,713,000
Fair value measured on recurring basis \| Total \| U.S. agency
Assets measured at Fair Value
Available-for-sale securities	8,588,000	11,759,000
Fair value measured on recurring basis \| Total \| Municipal
Assets measured at Fair Value
Available-for-sale securities	498,191,000	432,319,000
Fair value measured on recurring basis \| Total \| Equity
Assets measured at Fair Value
Available-for-sale securities	$ 416,814,000	$ 375,788,000

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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