ACCUMULATED OTHER COMPREHENSIVE INCOME (Schedule of Components) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 1,692,940	$ 1,496,752	$ 1,496,752
Other comprehensive income before reclassifications	24,782		14,064
Amounts reclassified from accumulated other comprehensive income	(636)		(1,503)
Net other comprehensive income/(loss)	24,146		12,561
Ending balance	1,736,173		1,692,940
Foreign currency translation gains
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	15,975	8,559	8,559
Other comprehensive income before reclassifications	7,496		7,416
Amounts reclassified from accumulated other comprehensive income	0		0
Net other comprehensive income/(loss)	7,496		7,416
Ending balance	23,471		15,975
Net investment hedges of New Zealand JV
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1,665	1,665	1,665
Other comprehensive income before reclassifications	110		0
Amounts reclassified from accumulated other comprehensive income	0		0
Net other comprehensive income/(loss)	110		0
Ending balance	1,775		1,665
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	16,184	10,831	10,831
Other comprehensive income before reclassifications	17,176		7,321
Amounts reclassified from accumulated other comprehensive income	(795)	(404)	(1,968)
Net other comprehensive income/(loss)	16,381		5,353
Ending balance	32,565		16,184
Cash flow hedges | Interest rate swaps
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income before reclassifications	15,600
Employee benefit plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(20,407)	(20,199)	(20,199)
Other comprehensive income before reclassifications	0		(673)
Amounts reclassified from accumulated other comprehensive income	159		465
Net other comprehensive income/(loss)	159		(208)
Ending balance	(20,248)		(20,407)
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	13,417	$ 856	856
Ending balance	$ 37,563		$ 13,417