RETIREMENT ANNUITY AND GUARANTEED CONTINUOUS EMPLOYMENT PLANS (Changes in Fair Value of Level 3 Pension Plan Assets) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Retirement Annuity and Guaranteed Continuous Employment Plans
Balance at the beginning of year		$ 1,010,937	$ 939,995
Realized and unrealized gains		9,298	108,060
Balance at the end of year		576,101	1,010,937
Significant Unobservable Inputs (Level 3)
Retirement Annuity and Guaranteed Continuous Employment Plans
Balance at the beginning of year		38,015
Balance at the end of year		40,401	38,015
Private equity funds
Retirement Annuity and Guaranteed Continuous Employment Plans
Balance at the beginning of year	[1]	38,015
Balance at the end of year	[1]	40,401	38,015
Private equity funds | Significant Unobservable Inputs (Level 3)
Retirement Annuity and Guaranteed Continuous Employment Plans
Balance at the beginning of year		38,015
Purchases, sales, issuances and settlements		(2,253)
Realized and unrealized gains		4,639
Balance at the end of year		40,401	$ 38,015
The amount of total gains during the period attributable to the change in unrealized gains relating to Level 3 net assets still held at the reporting date		$ 1,111

[1] Private equity funds consist of four funds seeking capital appreciation by investing in private equity investment partnerships and venture capital companies. Funds are comprised of unrestricted and restricted publicly traded securities and privately held securities. Unrestricted securities are valued at the closing market price on the reporting date. Restricted securities may be valued at a discount from such closing public market price, depending on facts and circumstances. Privately held securities are valued at fair value as determined by the fund directors and general partners.