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SHAREHOLDERS' EQUITY - Share repurchase activities (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	5 Months Ended	12 Months Ended
	Jan. 15, 2016	Aug. 20, 2015	Aug. 31, 2015	Jan. 15, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accelerated Share Repurchase Agreement August 17 2015
Treasury Shares [Line Items]
Total shares (in shares)	1,358,380	4,149,378	4,149,378	5,507,758		1,358,380	4,149,378
Total cost			$ 300,000
Average price per share (in usd per share)				$ 54.47
Common stocks
Treasury Shares [Line Items]
Total shares (in shares)					4,288,000	10,508,000	4,616,000
Total cost					$ 285,858	$ 571,805	$ 264,538
Average price per share (in usd per share)					$ 66.67	$ 54.42	$ 57.32
Common stocks | In the open market
Treasury Shares [Line Items]
Total shares (in shares)					3,932,000	10,241,000	4,264,000
Total cost					$ 261,180	$ 557,476	$ 246,490
Average price per share (in usd per share)					$ 66.43	$ 54.44	$ 57.80
Common stocks | From employees
Treasury Shares [Line Items]
Total shares (in shares)					356,000	267,000	352,000
Total cost					$ 24,678	$ 14,329	$ 18,048
Average price per share (in usd per share)					$ 69.36	$ 53.74	$ 51.34

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Total cost of shares repurchased divided by the total number of shares repurchased.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
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-SubTopic 10
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Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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