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Revenue Recognition Details 1 (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Revenue from Contract with Customer [Abstract]        
Cumulative Effect on Retained Earnings, before Tax   $ 0    
Unbilled Contracts Receivable $ 16,200,000   $ 12,400,000  
Deferred Revenue 128,962,000 130,704,000 $ 105,381,000 $ 107,166,000
Customer pre-payments/deferred revenue 167,599,000 151,009,000    
Contract with Customer, Liability, Revenue Recognized (144,303,000) (129,796,000)    
Temporary Equity, Foreign Currency Translation Adjustments $ 285,000 $ 2,325,000    
Revenue, Remaining Performance Obligation, Optional Exemption, Performance Obligation [true false] true