Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2013

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, 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	)

	As of December 31, 2012
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	126,570	$	126,570	$	—	$	—		0.01	%
Corporate notes, bonds and commercial paper	57,345		57,356		4		(15		)	0.17	%
Total cash equivalents and marketable securities	183,915		183,926		4		(15		)
Cash	19,415		19,415		—		—
Total cash, cash equivalents and marketable securities	$	203,330	$	203,341	$	4	$	(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, 2013		December 31, 2012
	(Dollars in thousands)
Cash equivalents	$	310,131	$	129,569
Short term marketable securities	48,966		54,346
Total cash equivalents and marketable securities	359,097		183,915
Cash	28,565		19,415
Total cash, cash equivalents and marketable securities	$	387,662	$	203,330

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, 2013 and 2012 are as follows:

	Fair Value				Gross Unrealized Loss
	December 31, 2013		December 31, 2012		December 31, 2013			December 31, 2012
	(In thousands)
Less than one year
Corporate notes, bonds and commercial paper	$	53,491	$	51,819	$	(15	)	$	(15	)