Fair Value Measurements

12 Months Ended

Dec. 31, 2012

Fair Value Disclosures [Abstract]

Fair Value Measurements

Fair Value Measurements

The Company’s assets that are measured at fair value on a recurring basis, at December 31, 2012 and 2011, consist of the following:

			Fair Value Measurements at Reporting Date Using
At December 31, 2012	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Unrestricted
Available-for-sale marketable securities:
U.S. government and government agency obligations	$	328,146			$	328,146
Municipal bonds	17,510				17,510
Equity security	3,393		$	3,393
	349,049		3,393		345,656
Restricted
Available-for-sale marketable securities:
U.S. government obligations	5,909				5,909
	$	354,958	$	3,393	$	351,565
At December 31, 2011
Unrestricted
Available-for-sale marketable securities:
U.S. government and government agency obligations	$	284,819			$	284,819
U.S. government guaranteed corporate bonds	15,317				15,317
U.S. government guaranteed collateralized mortgage obligations	623				623
Municipal bonds	15,326				15,326
Mortgage-backed securities	115				115
Equity security	3,019		$	3,019
	319,219		3,019		316,200
Restricted
Available-for-sale marketable securities:
U.S. government obligations	5,940				5,940
	$	325,159	$	3,019	$	322,140

Marketable securities included in Level 2 were valued using a market approach utilizing prices and other relevant information, such as interest rates, yield curves, prepayment speeds, loss severities, credit risks and default rates, generated by market transactions involving identical or comparable assets. The Company considers market liquidity in determining the fair value for these securities. The Company did not record any charges for other-than-temporary impairment of its Level 2 marketable securities in 2012 and 2011, and recorded an impairment charge in 2010 which was not material.

The Company holds one Level 3 marketable security, which had a fair value of $0 at December 31, 2012 and December 31, 2011. This Level 3 security was valued using information provided by the Company’s investment advisors and other sources, including quoted bid prices which took into consideration the security’s lack of liquidity. There were no purchases, sales, or maturities of Level 3 marketable securities and no unrealized gains or losses related to Level 3 marketable securities for the years ended December 31, 2012 and 2011. There were no transfers of marketable securities between Levels 1, 2, or 3 classifications during the years ended December 31, 2012 and 2011.

As of December 31, 2012, the Company had $400.0 million in aggregate principal amount of 1.875% convertible senior notes that will mature on October 1, 2016 unless earlier converted or repurchased. The fair value of the outstanding convertible senior notes was estimated to be $843.2 million and $375.5 million as of December 31, 2012 and 2011, respectively, and was determined based on Level 2 inputs.