Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2015

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-Sale Investments

The following tables summarize our amortized cost, gross unrealized gains and losses and fair value of our available-for-sale investments in marketable securities (in thousands):

	September 30, 2015
			Gross		Gross
	Amortized		Unrealized		Unrealized			Aggregate
	Cost		Gains		Losses			Fair Value
U.S. government and government agency debt securities	$	196,828	$	86	$	(1	)	$	196,913
Corporate debt securities		214,276		50		(23	)		214,303
Total	$	411,104	$	136	$	(24	)	$	411,216
	December 31, 2014
			Gross		Gross
	Amortized		Unrealized		Unrealized			Aggregate
	Cost		Gains		Losses			Fair Value
U.S. government and government agency debt securities	$	405,049	$	68	$	(135	)	$	404,982
Corporate debt securities		611,950		39		(365	)		611,624
Total	$	1,016,999	$	107	$	(500	)	$	1,016,606

Fair Value of Available-for-Sale Marketable Securities by Contractual Maturities

The estimated fair value of available-for-sale marketable securities, classified by their contractual maturities was as follows (in thousands):

	September 30, 2015
Due within one year	$	406,701
After one year through three years		4,515
Total	$	411,216