FAIR VALUE MEASUREMENT AND FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets
Deferred compensation plan assets, carrying amount	$ 30,733	$ 30,726
Liabilities
Deferred compensation plan liabilities, carrying amount	27,766	25,581
2% Convertible senior notes due June 2022
Liabilities
2% convertible senior notes due June 2022, carrying amount	600,000	600,000
2% convertible senior notes due June 2022, fair value	536,472	602,250
Quoted Prices in Active Markets (Level 1)
Assets
Deferred compensation plan assets, carrying amount	0	0
Liabilities
Deferred compensation plan liabilities, carrying amount	0	0
Quoted Prices in Active Markets (Level 1) | 2% Convertible senior notes due June 2022
Liabilities
2% convertible senior notes due June 2022, fair value	536,472	602,250
Significant Other Observable Inputs (Level 2)
Assets
Deferred compensation plan assets, carrying amount	30,733	30,726
Liabilities
Deferred compensation plan liabilities, carrying amount	27,766	25,581
Significant Other Observable Inputs (Level 2) | 2% Convertible senior notes due June 2022
Liabilities
2% convertible senior notes due June 2022, fair value	0	0
Significant Unobservable Inputs (Level 3)
Assets
Deferred compensation plan assets, carrying amount	0	0
Liabilities
Deferred compensation plan liabilities, carrying amount	0	0
Significant Unobservable Inputs (Level 3) | 2% Convertible senior notes due June 2022
Liabilities
2% convertible senior notes due June 2022, fair value	$ 0	$ 0