FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets measured at fair value on a recurring basis
Initial notional amount		$ 250,000
Recurring
Assets measured at fair value on a recurring basis
Assets fair value disclosure	$ 5,752	5,729
Liabilities fair value disclosure	3,397	3,136
Recurring | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	3,397	3,136
Recurring | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,997	3,990
Recurring | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,755	1,739
Recurring | Quoted Prices in Active Markets (Level 1)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	2,156	2,139
Recurring | Quoted Prices in Active Markets (Level 1) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	401	400
Recurring | Quoted Prices in Active Markets (Level 1) | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,755	1,739
Recurring | Other Observable Inputs (Level 2)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,596	3,590
Liabilities fair value disclosure	3,397	3,136
Recurring | Other Observable Inputs (Level 2) | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	3,397	3,136
Recurring | Other Observable Inputs (Level 2) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	$ 3,596	$ 3,590