Annual report pursuant to Section 13 and 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Provisions for depreciation      
Depreciation $ 27,381 $ 24,725 $ 19,354
Buildings | Minimum      
Property, Plant and Equipment [Line Items]      
Useful lives of the assets 10 years    
Buildings | Maximum      
Property, Plant and Equipment [Line Items]      
Useful lives of the assets 40 years    
Furniture, fixtures, and operating equipment | Minimum      
Property, Plant and Equipment [Line Items]      
Useful lives of the assets 2 years    
Furniture, fixtures, and operating equipment | Maximum      
Property, Plant and Equipment [Line Items]      
Useful lives of the assets 10 years