The following table summarizes fair value measurements by level at December 31, 2013, for assets and liabilities measured at fair value on a recurring basis:



	Level I		Level II		Level III		Total
Assets
Cash and cash equivalents	$	974,304	$	—	$	—	$	974,304
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	212,185	$	12,238	$	—	$	224,423
Corporate securities	—		296,086		—		296,086
Municipal securities:
General obligation	—		54,422		—		54,422
Pre-refunded	—		10,917		—		10,917
Revenue	—		69,054		—		69,054
Variable rate demand notes	—		28,575		—		28,575
Asset backed securities	—		139,050		—		139,050
Mortgage backed securities	$	—	$	33,891	$	—	$	33,891
Total investments	$	212,185	$	644,233	$	—	$	856,418
Restricted deposits available for sale:
Cash and cash equivalents	$	26,642	$	—	$	—	$	26,642
Certificates of deposit	5,891		—		—		5,891
U.S. Treasury securities and obligations of U.S. government corporations and agencies	14,413		—		—		14,413
Total restricted deposits	$	46,946	$	—	$	—	$	46,946
Other long term assets:
Interest rate swap contract	$	—	$	9,576	$	—	$	9,576
Total assets at fair value	$	1,233,435	$	653,809	$	—	$	1,887,244

The following table summarizes fair value measurements by level at December 31, 2012, for assets and liabilities measured at fair value on a recurring basis:



	Level I		Level II		Level III		Total
Assets
Cash and cash equivalents	$	745,933	$	—	$	—	$	745,933
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	57,114	$	40,246	$	—	$	97,360
Corporate securities	—		295,111		—		295,111
Municipal securities:
General obligation	—		86,571		—		86,571
Pre-refunded	—		5,422		—		5,422
Revenue	—		84,064		—		84,064
Variable rate demand notes	—		23,385		—		23,385
Asset backed securities	—		74,637		—		74,637
Mortgage backed securities	—		—		—		—
Total investments	$	57,114	$	609,436	$	—	$	666,550
Restricted deposits available for sale:
Cash and cash equivalents	$	14,455	$	—	$	—	$	14,455
Certificates of deposit	5,890		—		—		5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies	13,941		—		—		13,941
Total restricted deposits	$	34,286	$	—	$	—	$	34,286
Other long term assets:
Interest rate swap contract	$	—	$	16,304	$	—	$	16,304
Total assets at fair value	$	837,333	$	625,740	$	—	$	1,463,073