Estimated Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Cash Equivalents and Marketable Securities

Cash Equivalents and Marketable Securities as of:

	(in thousands)
March 31, 2020	Level 1 (a)		Level 2 (b)		Level 3 (c)		Total
Money Market Funds Note (d)	$	502,461	$	—	$	—	$	502,461
Marketable Securities:
U.S. Government Sponsored Agencies	4,325		—		—		4,325
Total	$	506,786	$	—	$	—	$	506,786

	(in thousands)
December 31, 2019	Level 1 (a)		Level 2 (b)		Level 3 (c)		Total
Money Market Funds Note (d)	$	550,788	$	—	$	—	$	550,788
Marketable Securities:
U.S. Government Sponsored Agencies	4,550		—		—		4,550
Total	$	555,338	$	—	$	—	$	555,338

^(a) Level 1 - Financial instruments whose values are based on unadjusted quoted prices for identical assets or liabilities in an active market which the company has the ability to access at the measurement date.

^(b) Level 2 - Financial instruments whose values are based on quoted market prices in markets where trading occurs infrequently or whose values are based on quoted prices of instruments with similar attributes in active markets.

^(c) Level 3 - Financial instruments whose values are based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs reflect management's own assumptions about the assumptions a market participant would use in pricing the asset.

^(d) The money market funds noted above are included in cash and cash equivalents.

Schedule of Convertible Senior Notes

The carrying amounts and estimated fair values (Level 2) of debt instruments are as follows (in thousands):

	As of March 31, 2020				As of December 31, 2019
	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
Convertible Senior Notes	$	—	$	—	$	7,106	$	28,900

Schedule of Fair Value Measurement and Valuation Techniques

The following table summarizes the significant unobservable inputs in the fair value measurement of the liability related to the sale of future royalties as of March 31, 2020:

	Fair Value (in thousands)	Valuation Technique	Unobservable Input	Range	Weighted Average
Liability related to the sale of future royalties	$274,706	Discounted cash flow	Discount rate	16% - 26%	19%
			Future royalty payments	2020 to 2036