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
Mar. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months $ 592,080 $ 541,914
Unrealized Loss, Less Than 12 Months (1,389) (1,661)
Fair Value, Greater Than 12 Months 79,663 117,289
Unrealized Loss, Greater Than 12 Months (54) (110)
Fair Value 671,743 659,203
Unrealized Loss (1,443) (1,771)
Certificates of deposit    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 0 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 199 199
Unrealized Loss (1) (1)
Commercial paper    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 14,981 24,925
Unrealized Loss, Less Than 12 Months (3) (9)
Fair Value, Greater Than 12 Months 0 0
Unrealized Loss, Greater Than 12 Months 0 0
Fair Value 14,981 24,925
Unrealized Loss (3) (9)
Corporate notes and bonds    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 343,313 294,818
Unrealized Loss, Less Than 12 Months (761) (889)
Fair Value, Greater Than 12 Months 64,470 99,433
Unrealized Loss, Greater Than 12 Months (39) (79)
Fair Value 407,783 394,251
Unrealized Loss (800) (968)
U.S. Government agencies    
Schedule of Available-for-sale Securities [Line Items]    
Fair Value, Less Than 12 Months 233,786 222,171
Unrealized Loss, Less Than 12 Months (625) (763)
Fair Value, Greater Than 12 Months 14,994 17,657
Unrealized Loss, Greater Than 12 Months (14) (30)
Fair Value 248,780 239,828
Unrealized Loss $ (639) $ (793)