Short-term Investments (Tables)

9 Months Ended

Sep. 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, the category using the fair value hierarchy and where they are classified on the Consolidated Balance Sheets:

	As of September 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	$	920,513	$	—	$	—		$	920,513	$	917,936	$	—	$	2,577
Level 1 securities:
Money market funds	52,737		—		—			52,737		51,222		—		1,515
Level 2 securities:
Corporate debt securities	220,826		770		(68		)	221,528		—		221,528		—
Government securities	110,860		159		—			111,019		—		111,019		—
Certificates of deposit/commercial paper	9,817		—		—			9,817				9,817
Agency securities	31,770		4		(40		)	31,734		—		31,734		—
Total	$	1,346,523	$	933	$	(108	)	$	1,347,348	$	969,158	$	374,098	$	4,092

	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 September 30, 2016 is as follows:

	(in thousands)
Due within one year	$	80,355
Due after one year and through five years	293,743
Total short-term investments	$	374,098