FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2014
Interest rate swap agreement
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	$ 5,812	$ 5,787
Liabilities fair value disclosure	2,293	3,198
Recurring | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	2,293	3,198
Recurring | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	4,078	4,080
Recurring | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,734	1,707
Recurring | Quoted Prices in Active Markets (Level 1)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	2,738	2,314
Recurring | Quoted Prices in Active Markets (Level 1) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,004	607
Recurring | Quoted Prices in Active Markets (Level 1) | Money market funds
Assets measured at fair value on a recurring basis
Assets fair value disclosure	1,734	1,707
Recurring | Other Observable Inputs (Level 2)
Assets measured at fair value on a recurring basis
Assets fair value disclosure	3,074	3,473
Liabilities fair value disclosure	2,293	3,198
Recurring | Other Observable Inputs (Level 2) | Interest rate swap agreement
Assets measured at fair value on a recurring basis
Liabilities fair value disclosure	2,293	3,198
Recurring | Other Observable Inputs (Level 2) | Fixed-income securities
Assets measured at fair value on a recurring basis
Assets fair value disclosure	$ 3,074	$ 3,473