Short-term Investments (Tables)

12 Months Ended

Dec. 31, 2015

Short-term Investments [Abstract]

Available-For-Sale Securities Reported at Fair Value

The following tables summarize, by major security type, the Company’s assets that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy and where they are classified on the Consolidated Balance Sheets.

	As of December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cash and cash equivalents		Short-term investments		Non-current assets (1)
	(in thousands)
Cash	$	1,708,220	$	—	$	—		$	1,708,220	$	1,706,592	$	—	$	1,628
Level 1 securities:
Money market funds	107,199		—		—			107,199		102,738		—		4,461
Level 2 securities:
Corporate debt securities	240,867		154		(409		)	240,612		—		240,612		—
Government securities	235,252		—		(1,046		)	234,206		—		234,206		—
Agency securities	26,576		—		(9		)	26,567		—		26,567		—
Total	$	2,318,114	$	154	$	(1,464	)	$	2,316,804	$	1,809,330	$	501,385	$	6,089

	As of December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Cash and cash equivalents		Short-term investments		Non-current assets (1)
	(in thousands)
Cash	$	1,007,543	$	—	$	—		$	1,007,543	$	1,007,543	$	—	$	—
Level 1 securities:
Money market funds	111,759		—		—			111,759		106,065		—		5,694
Level 2 securities:
Corporate debt securities	295,500		432		(199		)	295,733		—		295,733		—
Government securities	168,749		120		(95		)	168,774		—		168,774		—
Asset and mortgage-backed securities	112		—		—			112		—		112		—
Certificate of deposits	3,600		—		—			3,600		—		3,600		—
Agency securities	26,665		5		(1		)	26,669		—		26,669		—
Total	$	1,613,928	$	557	$	(295	)	$	1,614,190	$	1,113,608	$	494,888	$	5,694

(1) Primarily restricted cash that is related to workers compensation deposits and letter of credit agreements.

Estimated Fair Value of Short-Term Investments by Contractual Maturity

The estimated fair value of short-term investments by contractual maturity as of December 31, 2015 is as follows:

	(in thousands)
Due within one year	$	137,927
Due after one year and through 5 years	363,458
Total short-term investments	$	501,385