Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2013

Available-for-sale Securities [Abstract]

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

All cash equivalents and marketable securities are classified as available-for-sale. Total cash, cash equivalents and marketable securities are summarized as follows:

	As of March 31, 2013
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	139,768	$	139,768	$	—	$	—		0.01	%
Corporate notes, bonds and commercial paper	58,614		58,638		—		(24		)	0.15	%
Total cash equivalents and marketable securities	198,382		198,406		—		(24		)
Cash	16,446		16,446		—		—
Total cash, cash equivalents and marketable securities	$	214,828	$	214,852	$	—	$	(24	)

	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
	March 31, 2013		December 31, 2012
	(Dollars in thousands)
Cash equivalents	$	140,769	$	129,569
Short term marketable securities	57,613		54,346
Total cash equivalents and marketable securities	198,382		183,915
Cash	16,446		19,415
Total cash, cash equivalents and marketable securities	$	214,828	$	203,330

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

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 March 31, 2013 and December 31, 2012 are as follows:

	Fair Value				Gross Unrealized Loss
	March 31, 2013		December 31, 2012		March 31, 2013			December 31, 2012
	(In thousands)
Less than one year
Corporate notes, bonds and commercial paper	$	58,590	$	51,819	$	(24	)	$	(15	)