Short-term Investments (Tables)

6 Months Ended

Jun. 30, 2016

Short-Term Investments And Fair Value Measurement [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 June 30, 2016
	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	$	851,449	$	—	$	—		$	851,449	$	848,875	$	—	$	2,574
Level 1 securities:
Money market funds	543,564		—		—			543,564		542,050		—		1,514
Level 2 securities:
Corporate debt securities	200,366		1,195		(49		)	201,512		—		201,512		—
Government securities	230,815		759		—			231,574		—		231,574		—
Agency securities	10,209		8		—			10,217		—		10,217		—
Total	$	1,836,403	$	1,962	$	(49	)	$	1,838,316	$	1,390,925	$	443,303	$	4,088

	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

(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 June 30, 2016 is as follows:

	(in thousands)
Due within one year	$	144,035
Due after one year and through five years	299,268
Total short-term investments	$	443,303