EARNINGS PER SHARE (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income (Numerator)
Net income	$ 444,800	$ 32,566	$ 46,035	$ 70,703	$ 122,500	$ 52,033	$ 50,600	$ 25,629	$ 594,104	$ 250,762	$ 176,099
Net income attributable to noncontrolling interests									(18,091)	(5,461)	(4,575)
Numerator for diluted earnings available to common shareholders									$ 576,013	$ 245,301	$ 171,524
Shares (Denominator)
Weighted average common shares outstanding (in shares)									99,844	93,567	95,003
Dilutive effect of outstanding stock settled appreciation rights and stock options									945	866	725
Weighted-average common and common equivalent shares outstanding (in shares)									100,789	94,433	95,728
Antidilutive Securities Excluded from Computation
Antidilutive dilutive securities excluded from calculation of diluted earnings per share (in shares)									500	600	100