Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2015

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, 2015
(Dollars in thousands)	Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Weighted Rate of Return
Money market funds	$	77,804	$	77,804	$	—	$	—		0.12	%
U.S. Government bonds and notes	14,110		14,142		—		(32)			0.48	%
Corporate notes, bonds, commercial paper and other	160,823		160,979		—		(156)			0.45	%
Total cash equivalents and marketable securities	252,737		252,925		—		(188)
Cash	34,969		34,969		—		—
Total cash, cash equivalents and marketable securities	$	287,706	$	287,894	$	—	$	(188	)

	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	)

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, 2015		December 31, 2014
	(Dollars in thousands)
Cash equivalents	$	108,795	$	124,938
Short term marketable securities	143,942		145,983
Total cash equivalents and marketable securities	252,737		270,921
Cash	34,969		29,188
Total cash, cash equivalents and marketable securities	$	287,706	$	300,109

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, 2015 and 2014 are as follows:

	Fair Value				Gross Unrealized Loss
	December 31, 2015		December 31, 2014		December 31, 2015			December 31, 2014
	(In thousands)
Less than one year
Corporate notes, bonds and commercial paper	$	159,673	$	139,989	$	(188	)	$	(114	)