FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest rate swap agreement
Assets measured at fair value on a recurring basis
Initial notional amount			$ 250,000
Other Observable Inputs (Level 2) | Variable-rate debt
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	$ 285,200
Recurring
Assets measured at fair value on a recurring basis
Assets fair value disclosure	5,810	$ 5,748
Liabilities fair value disclosure	7,713	4,676
Recurring | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	7,713	4,676
Recurring | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	4,024	3,976
Recurring | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,786	1,772
Recurring | Quoted Prices in Active Markets (Level 1)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	2,604	2,175
Recurring | Quoted Prices in Active Markets (Level 1) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	818	403
Recurring | Quoted Prices in Active Markets (Level 1) | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,786	1,772
Recurring | Other Observable Inputs (Level 2)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,206	3,573
Liabilities fair value disclosure	7,713	4,676
Recurring | Other Observable Inputs (Level 2) | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	7,713	4,676
Recurring | Other Observable Inputs (Level 2) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	$ 3,206	$ 3,573