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CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)
Mar. 31, 2018
1.125% Call Option  
Percentage of contractual interest rate on derivative 1.125%
1.125% Conversion Option  
Percentage of contractual interest rate on derivative 1.125%
Convertible Notes | 1.625% Convertible Notes  
Percentage of contractual interest rate 1.625%