Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 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):

	June 30, 2016						December 31, 2015
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets:
Cash equivalents:
Money market funds	$	43,029	$	—	$	43,029	$	35,730	$	—	$	35,730
Commercial paper	—		58,481		58,481		—			63,890		63,890
Short-term investments:
Corporate debt securities	—			39,435		39,435	—			31,253		31,253
Corporate equity securities		—	2,769			2,769	—		—		—
Municipal bonds	—			1,413		1,413	—			2,763		2,763
U.S. government agency bonds	—			37,273		37,273	—			16,201		16,201
Asset-backed securities	—			12,244		12,244	—			11,443		11,443
Total	$	43,029	$	151,615	$	194,644	$	35,730	$	125,550	$	161,280

Carrying Value 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 and estimated fair value of our debt as of the indicated periods (in thousands):

	June 30, 2016				December 31, 2015
	Carrying		Fair		Carrying		Fair
	Value		Value		Value		Value
Credit agreement (carrying value including current maturities)	$	138,750	$	138,750	$	142,500	$	142,500
2010 Convertible debt (par value)		43,822		78,494		150,000		237,900
2016 Convertible debt (par value)		230,000		243,225	—		—