Estimated Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of cash equivalents and marketable securities

Cash equivalents and marketable securities as of:

	($ in thousands)
June 30, 2019	Level 1 (a)		Level 2 (b)		Level 3 (c)		Total
Money Market Funds Note (d)	$	330,422	$	—	$	—	$	330,422
Marketable Securities:
U.S. Government Sponsored Agencies	4,741		—		—		4,741
Total	$	335,163	$	—	$	—	$	335,163

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

^(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 June 30, 2019				As of December 31, 2018
	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
Convertible Senior Notes	$	7,081	$	19,600	$	7,055	$	20,100