Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2013

Fair Value Measurements

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 financial assets and liabilities measured at fair value on a recurring basis (in thousands):

	September 30, 2013							December31, 2012
	Level 1			Level 2		Total	Level 1				Level 2			Total
Assets:
Cash equivalents:
Money market funds	$	33,365	$	—	$	33,365	$		23,119	$		—	$		23,119
Commercial paper		—		20,798		20,798			—			35,856			35,856
Short-term investments:
Commercial paper		—		48,574		48,574			—			34,826			34,826
Municipal bonds		—		29,353		29,353			—			—			—
U.S. government agency bonds		—		23,235		23,235			—			748			748
Total	$	33,365	$	121,960	$	155,325	$		23,119	$		71,430	$		94,549
Liabilities:
Interest rate swap contracts (1)	$	—	$	377	$	377	$		—	$		1,069	$		1,069
Total	$	—	$	377	$	377	$		—	$		1,069	$		1,069

(1)As of September 30, 2013, the fair value of the interest rate swap contract was classified on our Balance Sheet in “Other current liabilities”. As of December31, 2012, the fair value of the interest rate swap contracts were classified on our Balance Sheet in “Other non-current liabilities”.

Carrying Value and Estimated Fair Value of Debt

We have chosen not to measure our debt at fair value.The following table indicates the carrying value and estimated fair value of our debt as of the indicated periods (in thousands):

	September30,2013				December31,2012
	Carrying Value		Fair Value		Carrying Value			Fair Value
Credit Agreement (carrying value including current maturities)	$	138,750	$	138,750		$	150,000		$	150,000
Convertible debt (par value)		150,000		182,355			150,000			158,400