FINANCIAL INSTRUMENTS AND FAIR VALUE | FINANCIAL INSTRUMENTS AND FAIR VALUE The following tables summarize our investments (in thousands): June 30, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt securities $ 429,112 $ 78 $ (736 ) $ 428,454 Commercial paper 87,464 1 (26 ) 87,439 U.S. government and agency securities 50,283 — (127 ) 50,156 Municipal bonds 45,390 21 (56 ) 45,355 Term deposit (1) 405 — — 405 Total available-for-sale securities $ 612,654 $ 100 $ (945 ) $ 611,809 December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt securities $ 379,494 $ 43 $ (925 ) $ 378,612 Commercial paper 95,110 23 (25 ) 95,108 U.S. government and agency securities 64,604 16 (79 ) 64,541 Municipal bonds 59,257 3 (235 ) 59,025 Certificates of deposit and term deposits (1) 4,219 — — 4,219 Total available-for-sale securities $ 602,684 $ 85 $ (1,264 ) $ 601,505 (1) The majority of our certificates of deposit and term deposits are foreign deposits. The following tables show the gross unrealized losses and the related fair values of our investments that have been in a continuous unrealized loss position (in thousands): June 30, 2017 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 346,768 $ (708 ) $ 14,738 $ (28 ) $ 361,506 $ (736 ) U.S. government and agency securities 47,668 (127 ) — — 47,668 (127 ) Municipal bonds 24,032 (56 ) — — 24,032 (56 ) Commercial paper 42,050 (26 ) — — 42,050 (26 ) Total available-for-sale securities $ 460,518 $ (917 ) $ 14,738 $ (28 ) $ 475,256 $ (945 ) December 31, 2016 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 311,980 $ (910 ) $ 13,541 $ (15 ) $ 325,521 $ (925 ) Municipal bonds 52,200 (235 ) — — 52,200 (235 ) U.S. government and agency securities 33,430 (79 ) — — 33,430 (79 ) Commercial paper 17,394 (25 ) — — 17,394 (25 ) Total available-for-sale securities $ 415,004 $ (1,249 ) $ 13,541 $ (15 ) $ 428,545 $ (1,264 ) The contractual maturities of our investments were as follows (in thousands): June 30, December 31, Due within one year $ 354,187 $ 376,522 Due between one and three years 257,622 224,983 Total $ 611,809 $ 601,505 Available-for-sale securities are reported at fair value, with unrealized gains and losses and the related tax impact included as a separate component of stockholders’ equity and in comprehensive income (loss). Realized gains and losses on available-for-sale securities are insignificant in the periods presented and are included in Other income (expense)—net in our condensed consolidated statements of operations. We use the specific identification method to determine the cost basis of investments sold. The unrealized losses on our available-for-sale securities were caused by fluctuations in market value and interest rates as a result of the economic environment. As the decline in market value are attributable to changes in market conditions and not credit quality, and because we have concluded currently that we neither intend to sell nor is it more likely than not that we will be required to sell these investments prior to a recovery of par value, we do not consider these investments to be other-than temporarily impaired as of June 30, 2017 . Fair Value Accounting—We apply the following fair value hierarchy for disclosure of the inputs used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities. Level 2—Inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the assets or liabilities, either directly or indirectly through market corroboration, for substantially the full term of the financial instruments. Level 3—Unobservable inputs based on our own assumptions used to measure assets and liabilities at fair value. The inputs require significant management judgment or estimation. We measure the fair value of money market funds and certain U.S. government and agency securities using quoted prices in active markets for identical assets. The fair value of all other financial instruments was based on quoted prices for similar assets in active markets, or model driven valuations using significant inputs derived from or corroborated by observable market data. We classify investments within Level 1 if quoted prices are available in active markets for identical securities. We classify items within Level 2 if the investments are valued using model driven valuations using observable inputs such as quoted market prices, benchmark yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency. Investments are held by custodians who obtain investment prices from a third-party pricing provider that incorporates standard inputs in various asset price models. Fair Value of Financial Instruments Assets Measured at Fair Value on a Recurring Basis The following tables present the fair value of our financial assets measured at fair value on a recurring basis as of June 30, 2017 and December 31, 2016 (in thousands): June 30, 2017 December 31, 2016 Aggregate Fair Value Quoted Prices in Active Markets For Identical Assets Significant Other Observable Remaining Inputs Significant Other Unobservable Remaining Inputs Aggregate Fair Value Quoted Prices in Active Markets For Identical Assets Significant Other Observable Remaining Inputs Significant Other Unobservable Remaining Inputs (Level 1) (Level 2) (Level 3) (Level 1) (Level 2) (Level 3) Assets: Corporate debt securities $ 428,454 $ — $ 428,454 $ — $ 378,612 $ — $ 378,612 $ — Commercial paper 106,915 — 106,915 — 105,097 — 105,097 — U.S. government and agency securities 50,156 44,706 5,450 — 64,541 52,082 12,459 — Municipal bonds 45,355 — 45,355 — 59,025 — 59,025 — Money market funds 18,997 18,997 — — 38,649 38,649 — — Certificates of deposit and term deposits (1) 55,758 — 55,758 — 59,479 — 59,479 — Total $ 705,635 $ 63,703 $ 641,932 $ — $ 705,403 $ 90,731 $ 614,672 $ — Reported as: Cash equivalents $ 93,826 $ 103,898 Short-term investments 354,187 376,522 Long-term investments 257,622 224,983 Total $ 705,635 $ 705,403 (1) Subsequent to the issuance of our consolidated financial statements as of and for the year ended December 31, 2016, we determined that $55.3 million in 30-day term deposits, included within cash and cash equivalents in the consolidated balance sheet as of December 31, 2016, should have also been included as Level 2 investments in the fair value hierarchy table for financial assets and financial liabilities measured at fair value on a recurring basis. Accordingly, we have corrected the above table as of December 31, 2016, the effect of which is immaterial to the financial statements as a whole. There were no transfers between Level 1 and Level 2 of the fair value hierarchy during the six months ended June 30, 2017 . |