SHAREHOLDERS' EQUITY - Share repurchase activities (Details) - Common stocks - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Treasury Shares [Line Items]
Total shares (in shares)	200	4,288	10,508
Total cost	$ 10,080	$ 285,858	$ 571,805
Average price per share (in usd per share)	$ 50.40	$ 66.67	$ 54.42
In the open market
Treasury Shares [Line Items]
Total shares (in shares)	0	3,932	10,241
Total cost	$ 0	$ 261,180	$ 557,476
Average price per share (in usd per share)	$ 0.00	$ 66.43	$ 54.44
From employees
Treasury Shares [Line Items]
Total shares (in shares)	200	356	267
Total cost	$ 10,080	$ 24,678	$ 14,329
Average price per share (in usd per share)	$ 50.40	$ 69.36	$ 53.74