Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2014

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 consist of the following:

			Fair Value Measurements at Reporting Date Using
As of December 31, 2014	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Unrestricted
Corporate bonds	$	547,506	—		$	547,506
U.S. government and government agency obligations	28,553		—		28,553
Municipal bonds	37,038		—		37,038
Equity securities	7,379		$	7,379	—
	620,476		7,379		613,097
Restricted
Equity securities	91,439		—		91,439
	$	711,915	$	7,379	$	704,536
As of December 31, 2013
Available-for-sale marketable securities:
Unrestricted
Corporate bonds	$	369,193	—		$	369,193
U.S. government and government agency obligations	107,521		—		107,521
Commercial paper	23,944		—		23,944
Municipal bonds	36,921		—		36,921
International government agency obligations	2,008		—		2,008
Certificates of deposit	7,514		—		7,514
Equity securities	1,166		$	1,166	—
	$	548,267	$	1,166	$	547,101