Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Available-for-sale securities (Details)

v3.8.0.1
Summary of Significant Accounting Policies - Available-for-sale securities (Details)
 3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
security
Jun. 30, 2017
Sep. 30, 2017
USD ($)
security
Available-for-sale securities      
Aggregate Estimated Fair Value $ 85,630,000,000   $ 85,630,000,000
Proceeds from the maturity or redemption of available for sales securities 7,032,000   7,032,000
Realized gains or losses $ 0   $ 0
Number of Available for Sale Securities in an unrealized loss position | security 39   39
Cash equivalents      
Available-for-sale securities      
Amortized cost $ 1,099,000   $ 1,099,000
Gross Unrealized Losses 20,000   20,000
Foreign currency translation adjustment 20,000   20,000
Aggregate Estimated Fair Value 1,099,000   1,099,000
Marketable securities      
Available-for-sale securities      
Amortized cost 86,575,000   86,575,000
Gross Unrealized Gains 1,000   1,000
Gross Unrealized Losses 2,774,000   2,774,000
Foreign currency translation adjustment 2,730,000   2,730,000
Aggregate Estimated Fair Value 86,532,000   86,532,000
Commercial Paper Maturity Period Less Than Three Months | Cash equivalents      
Available-for-sale securities      
Amortized cost 1,099,000   1,099,000
Gross Unrealized Losses 20,000   20,000
Foreign currency translation adjustment 20,000   20,000
Aggregate Estimated Fair Value 1,099,000   1,099,000
Corporate Debt Securities Maturity Period One Year or Less      
Available-for-sale securities      
Gross Unrealized Losses 0   0
Corporate Debt Securities Maturity Period Three Months To One Year | Marketable securities      
Available-for-sale securities      
Amortized cost 86,575,000   86,575,000
Gross Unrealized Gains 1,000   1,000
Gross Unrealized Losses 2,774,000   2,774,000
Foreign currency translation adjustment 2,730,000   2,730,000
Aggregate Estimated Fair Value $ 86,532,000   $ 86,532,000
Minimum | Corporate Debt Securities Maturity Period Three Months To One Year | Marketable securities      
Available-for-sale securities      
Available For Sale Securities Debt Maturity Period     3 months
Maximum      
Available-for-sale securities      
Available For Sale Securities Debt Maturity Period     1 year
Maximum | Commercial Paper Maturity Period Less Than Three Months | Cash equivalents      
Available-for-sale securities      
Available For Sale Securities Debt Maturity Period   3 months  
Maximum | Corporate Debt Securities Maturity Period Three Months To One Year | Marketable securities      
Available-for-sale securities      
Available For Sale Securities Debt Maturity Period     1 year