Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2016

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):

	September 30, 2016						December 31, 2015
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets:
Cash equivalents:
Money market funds	$	22,253	$	—	$	22,253	$	35,730	$	—	$	35,730
Commercial paper	—			20,492	20,492		—			17,245		17,245
Short-term investments:
Corporate debt securities	—			83,978		83,978	—			77,898		77,898
Corporate equity securities		—		2,476		2,476	—		—		—
Municipal bonds	—			1,410		1,410	—			2,763		2,763
U.S. government agency bonds	—			26,540		26,540	—			16,201		16,201
Asset-backed securities	—			11,513		11,513	—			11,443		11,443
Total	$	22,253	$	146,409	$	168,662	$	35,730	$	125,550	$	161,280

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):

	September 30, 2016				December 31, 2015
	Carrying		Fair		Carrying		Fair
	Value		Value		Value		Value
Credit agreement (carrying value including current maturities)	$	136,875	$	136,875	$	142,500	$	142,500
2010 Convertible debt		34,732		63,990		150,000		237,900
2016 Convertible debt		230,000		250,988	—		—