Short-term Investments (Tables)

3 Months Ended

Mar. 31, 2017

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 March 31, 2017
	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	$	1,073,756	$	—	$	—		$	1,073,756	$	1,070,361	$	—	$	3,395
Level 1 securities:
Money market funds	8,730				—			8,730		7,463		—		1,267
Level 2 securities:
Corporate debt securities	204,507		177		(592		)	204,092		—		204,092		—
Government securities	35,925		—		(142		)	35,783		—		35,783		—
Certificates of deposit/commercial paper	2,180		—		—			2,180				2,180
Agency securities	21,566		—		(216		)	21,350		—		21,350		—
Total	$	1,346,664	$	177	$	(950	)	$	1,345,891	$	1,077,824	$	263,405	$	4,662

	As of December 31, 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	$	1,267,523	$	—	$	—		$	1,267,523	$	1,264,126	$	—	$	3,397
Level 1 securities:
Money market funds	204,967		—					204,967		203,450		—		1,517
Level 2 securities:
Corporate debt securities	199,843		110		(731		)	199,222		—		199,222		—
Government securities	35,944		—		(128		)	35,816		—		35,816		—
Certificates of deposit	9,833		—		—			9,833				9,833
Agency securities	21,563				(228		)	21,335		—		21,335		—
Total	$	1,739,673	$	110	$	(1,087	)	$	1,738,696	$	1,467,576	$	266,206	$	4,914

(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 March 31, 2017 is as follows:

	(in thousands)
Due within one year	$	37,228
Due after one year and through five years	226,177
Total short-term investments	$	263,405