Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2011

Fair Value Measurements [Abstract]

Fair Value Measurements By Level For Assets Measured At Fair Value On A Recurring Basis

The following table summarizes fair value measurements by level at December 31, 2011, for assets and liabilities measured at fair value on a recurring basis:

	Level I		Level II		Level III		Total
Assets
Cash and cash equivalents	$	573,698	$	—	$	—	$	573,698
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	17,091	$	5,395	$	—	$	22,486
Corporate securities		—		189,029		—		189,029
Municipal securities:
General obligation		—		129,608		—		129,608
Pre-refunded		—		33,712		—		33,712
Revenue		—		120,860		—		120,860
Variable rate demand notes		—		64,658		—		64,658
Asset backed securities		—		52,192		—		52,192
Total investments	$	17,091	$	595,454	$	—	$	612,545
Restricted deposits available for sale:
Cash and cash equivalents	$	13,775	$	—	$	—	$	13,775
Certificates of deposit		5,890		—		—		5,890
U.S. Treasury securities and obligations of U.S. government corporations and agencies		7,153		—		—		7,153
Total restricted deposits	$	26,818	$	—	$	—	$	26,818
Interest rate swap contract	$	—	$	11,431	$	—	$	11,431
Total assets at fair value	$	617,607	$	606,885	$	—	$	1,224,492

The following table summarizes fair value measurements by level at December 31, 2010, for assets and liabilities measured at fair value on a recurring basis:

	Level I		Level II		Level III		Total
Assets
Cash and cash equivalents	$	434,166	$	—	$	—	$	434,166
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	14,809	$	7,096	$	—	$	21,905
Corporate securities		—		200,115		—		200,115
Municipal securities:
General obligation		—		113,461		—		113,461
Pre-refunded		—		33,198		—		33,198
Revenue		—		102,964		—		102,964
Variable rate demand notes		—		106,540		—		106,540
Asset backed securities		—		17,591		—		17,591
Total investments	$	14,809	$	580,965	$	—	$	595,774
Restricted deposits available for sale:
Cash and cash equivalents	$	8,814	$	—	$	—	$	8,814
Certificates of deposit		6,814		—		—		6,814
U.S. Treasury securities and obligations of U.S. government corporations and agencies		7,130		—		—		7,130
Total restricted deposits	$	22,758	$	—	$	—	$	22,758
Total assets at fair value	$	471,733	$	580,965	$	—	$	1,052,698