Marketable Securities, Fair Value (Details) (USD $)			12 Months Ended		12 Months Ended
	Dec. 31, 2011 Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2010 Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2010 Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2009 Fair Value Measurements at Reporting Date Using Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Fair Value Measurements at Reporting Date Using Significant Unobservable Inputs (Level 3) [Member] Integer	Dec. 31, 2010 Fair Value Measurements at Reporting Date Using Significant Unobservable Inputs (Level 3) [Member] Integer	Dec. 31, 2011 Unrestricted [Member]	Dec. 31, 2010 Unrestricted [Member]	Dec. 31, 2011 Unrestricted [Member] Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2010 Unrestricted [Member] Fair Value Measurements at Reporting Date Using Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2011 Unrestricted [Member] Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2010 Unrestricted [Member] Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Restricted [Member]	Dec. 31, 2010 Restricted [Member]	Dec. 31, 2011 Restricted [Member] Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2010 Restricted [Member] Fair Value Measurements at Reporting Date Using Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2011 Measured on a Recurring Basis [Member]	Dec. 31, 2010 Measured on a Recurring Basis [Member]
Available-for-sale marketable securities
U.S. government obligations								$ 284,819,000	$ 434,367,000			$ 284,819,000	$ 434,367,000	$ 5,940,000	$ 7,039,000	$ 5,940,000	$ 7,039,000
U.S. government guaranteed corporate bonds								15,316,000	64,008,000			15,316,000	64,008,000
U.S. government guaranteed collateralized mortgage obligations								622,000	2,131,000			622,000	2,131,000
Municipal bonds								15,326,000	1,603,000			15,326,000	1,603,000
Mortgage-backed securities								115,000	1,128,000			115,000	1,128,000
Equity security								3,019,000	3,612,000	3,019,000	3,612,000
Total available-for-sale marketable securities	3,019,000	3,612,000	510,276,000	322,138,000		0	0	319,217,000	506,849,000	3,019,000	3,612,000	316,198,000	503,237,000					325,157,000	513,888,000
Impaired securities [Abstract]
Number of marketable securities held						1	1
Other-than-temporary impairment charge			$ 100,000		$ 100,000