Invesments (Tables)

12 Months Ended

Dec. 31, 2014

Investments

Schedule of available-for-sale securities

			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
	(in thousands)
December 31, 2014
U.S. treasuries	$	81,506	$	27	$	(6	)	$	81,527
Corporate debt	39,031		20		(6		)	39,045
Total available-for-sale securities	$	120,537	$	47	$	(12	)	$	120,572
December 31, 2013
U.S. treasuries	$	130,956	$	22	$	(1	)	$	130,977
Government agency securities	61,004		9		—			61,013
Corporate debt	77,582		55		(36		)	77,601
Commercial paper	11,947		—		—			11,947
Total available-for-sale securities	$	281,489	$	86	$	(37	)	$	281,538

Schedule of available-for-sale securities in a loss position

	December 31, 2014					December 31, 2013
	Estimated		Gross			Estimated		Gross
	Fair		Unrealized			Fair		Unrealized
	Value		Losses			Value		Losses
	(in thousands)
U.S. treasuries	$	35,001	$	(6	)	$	29,068	$	(1	)
Corporate debt	13,069		(6		)	37,654		(36		)
Total	$	48,070	$	(12	)	$	66,722	$	(37	)

Schedule of contractual maturities of available-for-sale securities

	December 31, 2014
			Estimated
	Amortized		Fair
	Cost		Value
	(in thousands)
Due in one year or less	$	74,710	$	74,718
Due after one year through two years	45,827		45,854
Total	$	120,537	$	120,572