Marketable Securities

Marketable securities as of December 31, 2014 and December 31, 2013 consist of both debt securities issued by investment grade institutions as well as equity securities. The Company also held restricted marketable securities as of December 31, 2014, consisting of the Company's investment in Avalanche common shares (see Note 4), which were subject to customary transfer restrictions until January 2015 under a lock-up agreement with the underwriters of Avalanche's IPO.

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

The Company classifies its debt security investments based on their contractual maturity dates. The debt securities listed as of December 31, 2014 mature at various dates through August 2024. 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

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	)

During the year ended December 31, 2013, the Company recorded an other-than-temporary impairment charge of $2.9 million related to its investment in an equity security. There were no other-than-temporary impairment charges recorded on the Company's investments during 2014 or 2012.

Realized gains and losses are included as a component of investment income. For the year ended December 31, 2014, total realized gains on sales of marketable securities were $1.2 million, and there were no realized losses. For the year ended December 31, 2013, total realized gains on sales of marketable securities were $1.0 million, and there were no realized losses. For the year ended December 31, 2012, total realized gains and losses on sales of marketable securities were not material.

Changes in the Company's accumulated other comprehensive income (loss) for the years ended December 31, 2014, 2013, and 2012 related to unrealized gains and losses on available-for-sale marketable securities. For the years ended December 31, 2014 2013, and 2012, amounts reclassified from accumulated other comprehensive income (loss) into investment income in the Company's Statements of Operations were related to the impairment charge on the equity security and realized gains and losses on sales of marketable securities described above.