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STOCKHOLDERS' EQUITY (Details) (USD $)
 1 Months Ended 3 Months Ended 6 Months Ended
Mar. 31, 2013
Jun. 30, 2013
Jun. 30, 2013
Dec. 31, 2012
Equity [Abstract]        
At-the-market equity offering program, authorized amount $ 750,000,000      
At-the-market equity offering program, shares issued during period     1,128,700  
At-the-market equity offering program, proceeds from sale of stock during period   77,300,000 82,400,000  
At-the-market equity offering program, payments of stock issuance costs during period     1,300,000  
At-the-market equity offering program, remaining authorized offering amount   666,300,000 666,300,000  
Accumulated Other Comprehensive Income        
Foreign currency translation   18,628,000 18,628,000 23,441,000
Unrealized gain on marketable debt securities   0 0 807,000
Other   1,124,000 1,124,000 (894,000)
Total accumulated other comprehensive income   $ 19,752,000 $ 19,752,000 $ 23,354,000