Annual report pursuant to Section 13 and 15(d)

Debt (Credit Agreement) (Details)

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Debt (Credit Agreement) (Details) - USD ($)
12 Months Ended
Dec. 15, 2019
Nov. 19, 2015
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jul. 31, 2017
Jul. 18, 2017
Line of Credit Facility [Line Items]              
Revolving credit facility     $ 260,000,000 $ 0      
Effective interest rate     4.00%        
Repayments of convertible debt $ 184,751,000   $ 184,751,000 0 $ 0    
Second Amended and Restated Credit Agreement              
Line of Credit Facility [Line Items]              
Credit facility amount           $ 500,000,000  
Right to increase credit facility, amount           $ 150,000,000  
Letters of credit              
Line of Credit Facility [Line Items]              
Credit facility amount             $ 5,000,000
Credit Agreement              
Line of Credit Facility [Line Items]              
Revolving credit facility     $ 260,000,000 $ 0      
Voting equity of foreign subsidiary pledged   66.00%          
Non-voting equity of foreign subsidiary pledged   100.00%          
Commitment fee     0.25%        
Credit Agreement | Prepaid Expenses              
Line of Credit Facility [Line Items]              
Debt issuance cost, outstanding     $ 853,000        
Credit Agreement | Other non-current assets              
Line of Credit Facility [Line Items]              
Debt issuance costs, gross     2,103,000        
Debt issuance cost, outstanding     3,190,000        
Credit Agreement | Minimum | LIBOR              
Line of Credit Facility [Line Items]              
Spread on variable rate basis   1.50%          
Credit Agreement | Maximum | LIBOR              
Line of Credit Facility [Line Items]              
Spread on variable rate basis   3.25%          
Interest Expense | Credit Agreement              
Line of Credit Facility [Line Items]              
Write off of deferred debt issuance cost     $ 299,000