FAIR VALUE MEASUREMENTS (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Assets measured at fair value on a recurring basis
Initial notional amount	$ 250,000,000
Recurring
Assets measured at fair value on a recurring basis
Assets fair value disclosure	5,729,000	4,097,000
Liabilities fair value disclosure	3,136,000
Recurring | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	3,136,000
Recurring | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,990,000	4,006,000
Recurring | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,739,000	91,000
Recurring | Quoted Prices in Active Markets (Level 1)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	2,139,000	490,000
Recurring | Quoted Prices in Active Markets (Level 1) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	400,000	399,000
Recurring | Quoted Prices in Active Markets (Level 1) | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,739,000	91,000
Recurring | Other Observable Inputs (Level 2)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,590,000	3,607,000
Liabilities fair value disclosure	3,136,000
Recurring | Other Observable Inputs (Level 2) | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	3,136,000
Recurring | Other Observable Inputs (Level 2) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	$ 3,590,000	$ 3,607,000