Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value Disclosures [Abstract]

Schedule of assets measured at fair value on a recurring basis

The Company’s assets that are measured at fair value on a recurring basis, at March 31, 2013 and December 31, 2012, consist of the following:

			Fair Value Measurements at Reporting Date Using
At March 31, 2013	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	$	305,967			$	305,967
Corporate bonds	122,870				122,870
Commercial paper	25,172				25,172
Municipal bonds	17,161				17,161
Equity security	2,785		$	2,785
	473,955		2,785		471,170
Restricted
Available-for-sale marketable securities:
U.S. government obligations	8,358				8,358
	$	482,313	$	2,785	$	479,528
At December 31, 2012
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