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Long-Term Obligations and Commitments, Convertible Notes (Details)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Dec. 31, 2016
USD ($)
Nov. 30, 2014
USD ($)
Dec. 31, 2017
USD ($)
shares
$ / shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Mar. 31, 2017
Sep. 30, 2016
Convertible Notes [Abstract]              
Loss on early retirement of debt     $ 0 $ (3,983) $ 0    
Amortization of debt discount and debt issuance costs     32,500 25,100 $ 23,200    
Long-term debt $ 500,511   $ 533,111 $ 500,511      
1 Percent Convertible Senior Notes [Member]              
Convertible Notes [Abstract]              
Maturity date     Nov. 30, 2021        
Interest rate 1.00%   1.00% 1.00% 1.00% 1.00% 1.00%
Conversion price per share (in dollars per share) | $ / shares     $ 66.81        
Total shares of common stock subject to conversion (in shares) | shares     10,300,000        
Percentage of principal amount used a purchase price upon occurrence of fundamental change     100.00%        
Principal amount of convertible notes outstanding $ 685,450   $ 685,450 $ 685,450      
Unamortized portion of debt discount 175,699   144,112 175,699      
Long-term debt 500,511   533,111 500,511      
Carrying value of equity component 219,011   219,011 219,011      
1 Percent Convertible Senior Notes [Member] | Level 2 [Member]              
Convertible Notes [Abstract]              
Fair value of outstanding notes 700,969   $ 727,420 700,969      
1 Percent Convertible Senior Notes Issued in November 2014 [Member]              
Convertible Notes [Abstract]              
Face amount of offering   $ 500,000          
Proceeds from issuance of 1 percent convertible senior notes, net of issuance costs   487,000          
Issue date     Nov. 30, 2014        
Nonconvertible debt borrowing rate     7.40%        
Effective interest rate     7.80%        
Amortization period of debt discount     7 years        
1 Percent Convertible Senior Notes Issued in December 2016 [Member]              
Convertible Notes [Abstract]              
Face amount of offering 185,500     185,500      
Issue date     Dec. 31, 2016        
Nonconvertible debt borrowing rate     6.80%        
Effective interest rate     7.20%        
Amortization period of debt discount     5 years        
2 3/4 Percent Convertible Senior Notes [Member]              
Convertible Notes [Abstract]              
Principal amount repurchased 61,100 140,000   $ 61,100      
Repurchase of convertible senior notes   441,900          
Loss on early retirement of debt $ 3,983            
Interest rate 2.75%   2.75% 2.75% 2.75% 2.75% 2.75%
Principal amount of convertible notes outstanding   $ 61,200