Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2015

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, 2015						December 31, 2014
	Level 1			Level 2		Total	Level 1		Level 2		Total
Assets:
Cash equivalents:
Money market funds	$	10,146	$	—	$	10,146	$	9,785	$	—	$	9,785
Commercial paper		—		14,948		14,948		—		12,248		12,248
Short-term investments:
Corporate debt securities		—		69,620		69,620		—		88,494		88,494
Municipal bonds		—		1,353		1,353		—		9,945		9,945
U.S. government agency bonds		—		17,662		17,662		—		11,313		11,313
Asset-backed securities		—		10,463		10,463		—		10,336		10,336
Total	$	10,146	$	114,046	$	124,192	$	9,785	$	132,336	$	142,121

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, 2015				December 31, 2014
	Carrying Value		Fair Value		Carrying Value		Fair Value
Credit agreement (carrying value including current maturities)	$	146,250	$	146,250	$	120,000	$	120,000
Convertible debt (par value)		150,000		211,770		150,000		178,920