Short-term Investments	3 Months Ended
Mar. 31, 2019
Short Term Investments [Abstract]
Short-term Investments	(3) Short-term Investments The Company periodically invests a portion of its excess cash in short-term investment instruments. All of the Company’s short-term investments are in U.S. Treasury securities and all short-term investments have stated maturity dates between three months and one year from the purchase date. All short-term investments are included within “Short-term investments” on the accompanying Consolidated Balance Sheets. The fair value of the Company’s short-term investments is determined based on quoted market prices in active markets for identical securities (Level 1 inputs). As of March 31, 2019 and December 31, 2018, all short-term investments were classified as available-for-sale and reported at fair value. The amortized cost and fair value of available-for-sale investments at March 31, 2019 were $292.3 million and $292.3 million, respectively. The amortized cost and fair value of available-for-sale investments at December 31, 2018 were $466.6 million and $466.2 million, respectively. The total gross unrecognized holding losses accumulated in other comprehensive loss were not material as of March 31, 2019 and December 31, 2018. The total gross unrecognized holding gains accumulated in other comprehensive loss were not material as of March 31, 2019 and December 31, 2018. No other-than-temporary impairments related to these investments have been recognized as of March 31, 2019 and December 31, 2018.

Short-term Investments

3 Months Ended

Mar. 31, 2019

(3) Short-term Investments

The Company periodically invests a portion of its excess cash in short-term investment instruments. All of the Company’s short-term investments are in U.S. Treasury securities and all short-term investments have stated maturity dates between three months and one year from the purchase date. All short-term investments are included within “Short-term investments” on the accompanying Consolidated Balance Sheets. The fair value of the Company’s short-term investments is determined based on quoted market prices in active markets for identical securities (Level 1 inputs). As of March 31, 2019 and December 31, 2018, all short-term investments were classified as available-for-sale and reported at fair value.

The amortized cost and fair value of available-for-sale investments at March 31, 2019 were $292.3 million and $292.3 million, respectively. The amortized cost and fair value of available-for-sale investments at December 31, 2018 were $466.6 million and $466.2 million, respectively. The total gross unrecognized holding losses accumulated in other comprehensive loss were not material as of March 31, 2019 and December 31, 2018. The total gross unrecognized holding gains accumulated in other comprehensive loss were not material as of March 31, 2019 and December 31, 2018. No other-than-temporary impairments related to these investments have been recognized as of March 31, 2019 and December 31, 2018.