Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2017

The following table represents the fair value hierarchy based upon three levels of inputs, of which Levels 1 and 2 are considered observable and Level 3 is unobservable, for our financial assets and liabilities measured at fair value (in thousands):

	June 30, 2017						December 31, 2016
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets:
Cash equivalents:
Money market funds	$	14,625	$	—	$	14,625	$	6,531	$	—	$	6,531
Commercial paper	—			17,866		17,866	—			24,826		24,826
Short-term investments:
Corporate debt securities	—			96,858		96,858	—			109,140		109,140
U.S. government agency bonds	—			8,919		8,919	—			26,513		26,513
Asset-backed securities	—			14,066		14,066	—			14,494		14,494
Total	$	14,625	$	137,709	$	152,334	$	6,531	$	174,973	$	181,504

Carrying Value (Par Value for Convertible Debt) and Estimated Fair Value of Debt

We have chosen not to measure our debt at fair value, with changes recognized in earnings each reporting period. The following table indicates the carrying value (par value for convertible debt) and estimated fair value of our debt as of the indicated periods (in thousands):

	June 30, 2017				December 31, 2016
	Carrying		Fair		Carrying		Fair
	Value		Value		Value		Value
Credit agreement (carrying value including current maturities)	$	127,500	$	127,500	$	135,000	$	135,000
2010 Convertible debt (par value)		—		—		34,722		74,795
2016 Convertible debt (par value)		230,000		248,688		230,000		258,175