Annual report pursuant to Section 13 and 15(d)

Financial Instruments Financial Instruments - Additional Information (Details 4)

v3.8.0.1
Financial Instruments Financial Instruments - Additional Information (Details 4)
 12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
debt_security
Dec. 31, 2015
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Derivative Asset $ 734,000.000 $ 0 $ 0
Fair Value, Liabilities, Transfers between Levels 0    
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | debt_security   25  
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value   $ 42,200,000  
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax   39,000  
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings $ 734,000 $ 0  
Minimum [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Available For Sale Securities Non Current Maturity Period   1 year  
Maximum [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Period Of Unrealized Loss Position   12 months  
Available For Sale Securities Non Current Maturity Period   2 years  
Maximum [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value Inputs, Discount Rate   1.00%  
Investments [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax   $ 39,000