v3.7.0.1
Investments - Summary of Gross Unrealized Losses and Fair Value of Investments in a Continuous Unrealized Loss Position (Details) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months $ 603,443 $ 541,914
Unrealized Loss, Less Than 12 Months (1,320) (1,661)
Fair Value, Greater Than 12 Months 60,695 117,289
Unrealized Loss, Greater Than 12 Months (96) (110)
Fair Value 664,138 659,203
Unrealized Loss (1,416) (1,771)
Certificates of deposit    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 720 0
Unrealized Loss, Less Than 12 Months 0 0
Fair Value, Greater Than 12 Months 199 199
Unrealized Loss, Greater Than 12 Months (1) (1)
Fair Value 919 199
Unrealized Loss (1) (1)
Commercial paper    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 4,950 24,925
Unrealized Loss, Less Than 12 Months (8) (9)
Fair Value, Greater Than 12 Months 0 0
Unrealized Loss, Greater Than 12 Months 0 0
Fair Value 4,950 24,925
Unrealized Loss (8) (9)
Corporate notes and bonds    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 352,782 294,818
Unrealized Loss, Less Than 12 Months (643) (889)
Fair Value, Greater Than 12 Months 44,489 99,433
Unrealized Loss, Greater Than 12 Months (74) (79)
Fair Value 397,271 394,251
Unrealized Loss (717) (968)
U.S. Government agencies    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 244,991 222,171
Unrealized Loss, Less Than 12 Months (669) (763)
Fair Value, Greater Than 12 Months 16,007 17,657
Unrealized Loss, Greater Than 12 Months (21) (30)
Fair Value 260,998 239,828
Unrealized Loss $ (690) $ (793)