DERIVATIVE AND HEDGING INSTRUMENTS - Notional Amount of Derivatives Instruments (Details) - Cross Currency Interest Rate Swaps $ in Thousands, $ in Thousands	Sep. 30, 2018 USD ($)	Sep. 30, 2018 CAD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CAD ($)
Designated as Hedging Instrument | Cash Flow Hedges
Derivative [Line Items]
Notional amount	$ 845,000	$ 125,000	$ 845,000	$ 125,000
Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
Notional amount		55,425		56,300
Notional amount		125,000		125,000
Not Designated as Hedging Instrument | Net Investment Hedges
Derivative [Line Items]
Notional amount		$ 875		$ 0