Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2014

Available-for-sale Securities [Abstract]

Cash equivalents and marketable securities classified as available-for-sale

Total cash, cash equivalents and marketable securities are summarized as follows:



	As of December 31, 2014
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	124,938	$	124,938	$	—	$	—		0.01	%
Corporate notes, bonds and commercial paper	145,983		146,096		1		(114)			0.25	%
Total cash equivalents and marketable securities	270,921		271,034		1		(114)
Cash	29,188		29,188		—		—
Total cash, cash equivalents and marketable securities	$	300,109	$	300,222	$	1	$	(114	)



	As of December 31, 2013
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	300,605	$	300,605	$	—	$	—		0.01	%
Corporate notes, bonds and commercial paper	58,492		58,507		—		(15		)	0.15	%
Total cash equivalents and marketable securities	359,097		359,112		—		(15		)
Cash	28,565		28,565		—		—
Total cash, cash equivalents and marketable securities	$	387,662	$	387,677	$	—	$	(15	)

Available-for-sale securities reported at fair value

Available-for-sale securities are reported at fair value on the balance sheets and classified as follows:



	As of
	December 31, 2014		December 31, 2013
	(Dollars in thousands)
Cash equivalents	$	124,938	$	310,131
Short term marketable securities	145,983		48,966
Total cash equivalents and marketable securities	270,921		359,097
Cash	29,188		28,565
Total cash, cash equivalents and marketable securities	$	300,109	$	387,662

Estimated fair value of cash equivalents and marketable securities classified by date of contractual maturity and the length of time that the securities have been in a continuous unrealized loss position

The estimated fair value of cash equivalents and marketable securities classified by the length of time that the securities have been in a continuous unrealized loss position at December 31, 2014 and 2013 are as follows:



	Fair Value				Gross Unrealized Loss
	December 31, 2014		December 31, 2013		December 31, 2014			December 31, 2013
	(In thousands)
Less than one year
Corporate notes, bonds and commercial paper	$	139,989	$	53,491	$	(114	)	$	(15	)