SHAREHOLDERS' EQUITY - Accelerated share repurchase program (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	5 Months Ended	12 Months Ended
	Jan. 15, 2016	Aug. 31, 2015	Jan. 15, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Treasury Stock
Class of Stock [Line Items]
Total cost				$ 10,080	$ 285,858	$ 571,805
Additional paid-in capital
Class of Stock [Line Items]
Total cost				$ 0	$ 0	$ (60,000)
Accelerated Share Repurchase Agreement August 17 2015
Class of Stock [Line Items]
Total cost		$ 300,000
Total shares (in shares)	1,358,380	4,149,378	5,507,758		1,358,380
Accelerated Share Repurchases, initial repurchase percentage		80.00%
Average price per share (in usd per share)			$ 54.47
Accelerated Share Repurchase Agreement August 17 2015 | Treasury Stock
Class of Stock [Line Items]
Total cost	$ 60,000						$ 240,000
Accelerated Share Repurchase Agreement August 17 2015 | Additional paid-in capital
Class of Stock [Line Items]
Total cost							$ 60,000