SHARE-BASED PAYMENT - Compensation Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation costs
Share-based compensation	$ 21,134	$ 18,477	$ 14,084
Excess tax benefit recognized	9,545	631	1,410
Restricted shares
Compensation costs
Share-based compensation	12,336	10,272	8,214
Stock options
Compensation costs
Share-based compensation	1,570	1,768	1,957
2014 PSP | RSUs
Compensation costs
Share-based compensation	766	3,625	$ 3,913
2016 PSP | RSUs
Compensation costs
Share-based compensation	4,728	$ 2,812
2017 PSP | RSUs
Compensation costs
Share-based compensation	$ 1,734