Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2015

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 March 31, 2015	Cost Basis		Gains		Losses			Value
Unrestricted
Corporate bonds	$	530,693	$	898	$	(99	)	$	531,492
U.S. government and government agency obligations	56,433		201		—			56,634
Municipal bonds	39,807		52		(3		)	39,856
Equity securities	17,005		72,575		—			89,580
	$	643,938	$	73,726	$	(102	)	$	717,562
As of December 31, 2014
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

Marketable Securities, Based on Contractual Maturity Dates

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

	March 31, 2015		December 31, 2014
Maturities within one year	$	234,257	$	251,761
Maturities after one year through five years	392,624		360,208
Maturities after five years through ten years	1,101		1,128
	$	627,982	$	613,097

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 March 31, 2015	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate bonds	$	136,720	$	(85	)	$	4,139	$	(14	)	$	140,859	$	(99	)
Municipal bonds	3,938		(3		)	—		—			3,938		(3		)
	$	140,658	$	(88	)	$	4,139	$	(14	)	$	144,797	$	(102	)
As of December 31, 2014
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	)