Fair Value Measurements

12 Months Ended

Dec. 31, 2013

Fair Value Measurements

Fair Value Measurements

5. Fair Value Measurements

        We define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.

        Our valuation techniques are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect our market assumptions. We classify these inputs into the following hierarchy:

• Level 1—Quoted prices for identical instruments in active markets.

  Level 2—Quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations whose inputs are observable or whose significant value drivers are observable.

  Level 3—Unobservable inputs and little, if any, market activity for the assets.

        Our available-for-sale securities are measured at fair value on a recurring basis and our convertible subordinated notes are not measured at fair value on a recurring basis. The estimated fair values were as follows:

	Estimated Fair Value Measurements at Reporting Date Using:
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Types of Instruments (In thousands)	Level 1		Level 2		Level 3		Total
Assets at December 31, 2013:
U.S. government securities	$	42,158	$	—	$	—	$	42,158
U.S. government agency securities		98,236		43,095		—		141,331
U.S. corporate notes		61,591		33,386		—		94,977
U.S. commercial paper		3,499		98,523		—		102,022
Money market funds		122,343		—		—		122,343
Total assets measured at estimated fair value	$	327,827	$	175,004	$	—	$	502,831
Liabilities at December 31, 2013:
Convertible subordinated notes due 2023	$	—	$	408,250	$	—	$	408,250

	Estimated Fair Value Measurements at Reporting Date Using:
	Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Types of Instruments (In thousands)	Level 1		Level 2		Level 3		Total
Assets at December 31, 2012:
U.S. government securities	$	27,205	$	—	$	—	$	27,205
U.S. government agency securities		56,969		58,497		—		115,466
U.S. corporate notes		40,472		51,094		—		91,566
U.S. commercial paper		—		23,082		—		23,082
Money market funds		78,646		—		—		78,646
Total assets measured at estimated fair value	$	203,292	$	132,673	$	—	$	335,965
Liabilities at December 31, 2012:
Convertible subordinated notes due 2015	$	—	$	194,050	$	—	$	194,050

        At December 31, 2013, securities with a total fair value of $6.8 million were measured using Level 1 inputs in comparison to December 31, 2012, at which time the securities had a fair value of $7.0 million and were measured using Level 2 inputs. The transfer to Level 1 from Level 2 was primarily the result of increased trading volume of the securities at and around December 31, 2013, compared to December 31, 2012.

        At December 31, 2013, securities with a total fair value of $2.9 million were measured using Level 2 inputs in comparison to December 31, 2012, at which time the securities had a fair value of $2.9 million and were measured using Level 1 inputs. The transfer to Level 2 from Level 1 was primarily the result of decreased trading volume of the securities at and around December 31, 2013, compared to December 31, 2012.

        At December 31, 2012, there were no transfers from Level 1 to Level 2 or from Level 2 to Level 1 in comparison to December 31, 2011.