Estimated Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of Financial Instruments Recorded on Condensed Consolidated Balance Sheets

Cash Equivalents and Marketable Securities

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

	($ in thousands)
As of December 31, 2018	Level 1		Level 2		Level 3		Total
Money Market Funds Note (a)	$	326,239	$	—	$	—	$	326,239
Marketable Securities:
U.S. Government Sponsored Agencies	4,941		—		—		4,941
Total	$	331,180	$	—	$	—	$	331,180

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

Schedule of Carrying Amounts and Estimated Fair Values (Level 2) of Debt Instruments

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

	As of December 31, 2019				As of December 31, 2018
	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
Convertible Senior Notes	$	7,106	$	28,900	$	7,055	$	20,100