Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

The following tables summarize the Company's investments in marketable securities:

	Amortized		Unrealized					Fair
As of December 31, 2014	Cost Basis		Gains		Losses			Value
Unrestricted
Corporate bonds	$	548,832	$	136	$	(1,462	)	$	547,506
U.S. government and government agency obligations	28,596		3		(46		)	28,553
Municipal bonds	37,044		37		(43		)	37,038
Equity securities	2,005		5,374		—			7,379
	616,477		5,550		(1,551		)	620,476
Restricted
Equity securities	15,000		76,439		—			91,439
	$	631,477	$	81,989	$	(1,551	)	$	711,915

As of December 31, 2013
Unrestricted
Corporate bonds	$	369,321	$	233	$	(361	)	$	369,193
U.S. government and government agency obligations	107,493		55		(27		)	107,521
Commercial paper	23,891		53		—			23,944
Municipal bonds	36,935		45		(59		)	36,921
International government agency obligations	2,007		1		—			2,008
Certificates of deposit	7,509		5		—			7,514
Equity securities	1,166		—		—			1,166
	$	548,322	$	392	$	(447	)	$	548,267

Marketable Securities, Based on Contractual Maturity Dates

The fair values of debt security investments by contractual maturity consist of the following:

	As of December 31,
	2014		2013
Maturities within one year	$	251,761	$	158,376
Maturities after one year through five years	360,208		383,410
Maturities after five years through ten years	1,128		4,138
Maturities after ten years	—		1,177
	$	613,097	$	547,101

Fair Value and Unrealized Losses of Marketable Securities

The following table shows the fair value of the Company's marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position.

	Less than 12 Months					12 Months or Greater		Total
As of December 31, 2014	Fair Value		Unrealized Loss			Fair Value	Unrealized Loss	Fair Value		Unrealized Loss
Corporate bonds	$	390,613	$	(1,462	)	—	—	$	390,613	$	(1,462	)
U.S. government and government agency obligations	25,549		(46		)	—	—	25,549		(46		)
Municipal bonds	10,779		(43		)	—	—	10,779		(43		)
	$	426,941	$	(1,551	)	—	—	$	426,941	$	(1,551	)
As of December 31, 2013
Corporate bonds	$	176,140	$	(361	)	—	—	$	176,140	$	(361	)
U.S. government and government agency obligations	49,241		(27		)	—	—	49,241		(27		)
Municipal bonds	14,431		(59		)	—	—	14,431		(59		)
	$	239,812	$	(447	)	—	—	$	239,812	$	(447	)