Fair Value Measurements

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

Fair Value Measurements

The table below summarizes the Company's assets which are measured at fair value on a recurring basis. The following fair value hierarchy is used to classify assets, based on inputs to valuation techniques utilized to measure fair value:

• Level 1 - Quoted prices in active markets for identical assets

• Level 2 - Significant other observable inputs, such as quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model-based valuations in which significant inputs used are observable

• Level 3 - Significant other unobservable inputs

			Fair Value Measurements at Reporting Date
As of December 31, 2019	Fair Value		Level 1		Level 2
Available-for-sale debt securities:
Corporate bonds	$	3,988.1	—		$	3,988.1
U.S. government and government agency obligations	54.4		—		54.4
Sovereign bonds	27.3		—		27.3
Commercial paper	92.3		—		92.3
Certificates of deposit	72.4		—		72.4
Equity securities (unrestricted)	61.6		$	61.6	—
Equity securities (restricted)	557.2		557.2		—
	$	4,853.3	$	618.8	$	4,234.5
As of December 31, 2018
Available-for-sale debt securities:
Corporate bonds	$	2,718.4	—		$	2,718.4
U.S. government and government agency obligations	109.4		—		109.4
Sovereign bonds	7.6		—		7.6
Commercial paper	113.8		—		113.8
Certificates of deposit	60.0		—		60.0
Equity securities (unrestricted)	43.6		$	43.6	—
Equity securities (restricted)	44.4		—		44.4
	$	3,097.2	$	43.6	$	3,053.6

The Company held certain restricted equity securities as of December 31, 2019, including its investment in Alnylam (see Note 3), which are subject to transfer restrictions that expire at various dates through 2023.

The Company adopted ASU 2016-01 during the first quarter of 2018 (see Note 1); as a result, we recorded $118.3 million of net unrealized gains and $41.9 million of net unrealized losses on equity securities in Other income (expense), net for the years ended December 31, 2019 and 2018, respectively. During the year ended December 31, 2017, we recorded net unrealized gains of $14.7 million on equity securities in Other comprehensive income (loss).

In addition to the investments summarized in the table above, as of December 31, 2019 and 2018, the Company had $55.6 million and $45.5 million, respectively, in equity investments that do not have a readily determinable fair value. These investments are recorded within Other noncurrent assets.