Marketable Securities (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 354,990,000	$ 325,889,000
Unrealized Gains	670,000	530,000
Unrealized (Losses)	(702,000)	(1,260,000)
Total fair value of available-for-sale marketable securities	354,958,000	325,159,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Total	351,565,000	322,140,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	63,442,000	111,774,000
Fair Value - 12 Months or Greater	3,393,000	116,000
Fair Value - Total	66,835,000	111,890,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(51,000)	(1,108,000)
Unrealized Loss - 12 Months or Greater	(651,000)	(152,000)
Unrealized Loss - Total	(702,000)	(1,260,000)
Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	349,088,000	319,970,000
Unrealized Gains	661,000	509,000
Unrealized (Losses)	(700,000)	(1,260,000)
Total fair value of available-for-sale marketable securities	349,049,000	319,219,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Maturities within one year	77,819,000	43,333,000
Maturities after one year through five years	267,837,000	272,780,000
Maturities after five years through ten years		87,000
Total	345,656,000	316,200,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	62,248,000
Fair Value - 12 Months or Greater	3,393,000
Fair Value - Total	65,641,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(49,000)
Unrealized Loss - 12 Months or Greater	(651,000)
Unrealized Loss - Total	(700,000)
Restricted
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Maturities within one year	2,781,000	3,357,000
Maturities after one year through five years	3,128,000	2,583,000
Total	5,909,000	5,940,000
U.S. government and government agency obligations | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	327,502,000	284,458,000
Unrealized Gains	661,000	442,000
Unrealized (Losses)	(17,000)	(81,000)
Total fair value of available-for-sale marketable securities	328,146,000	284,819,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	44,738,000	103,529,000
Fair Value - Total	44,738,000	103,529,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(17,000)	(81,000)
Unrealized Loss - Total	(17,000)	(81,000)
U.S. government and government agency obligations | Restricted stock
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	1,194,000
Fair Value - Total	1,194,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(2,000)
Unrealized Loss - Total	(2,000)
U.S. government and government agency obligations | Restricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	5,902,000	5,919,000
Unrealized Gains	9,000	21,000
Unrealized (Losses)	(2,000)
Total fair value of available-for-sale marketable securities	5,909,000	5,940,000
U.S. government guaranteed corporate bonds | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		15,263,000
Unrealized Gains		54,000
Unrealized (Losses)
Total fair value of available-for-sale marketable securities		15,317,000
U.S. government guaranteed collateralized mortgage obligations | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		623,000
Unrealized Gains
Unrealized (Losses)
Total fair value of available-for-sale marketable securities		623,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months		623,000
Fair Value - Total		623,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months		(1,000)
Unrealized Loss - Total		(1,000)
Municipal bonds | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	17,542,000	15,314,000
Unrealized Gains		13,000
Unrealized (Losses)	(32,000)	(1,000)
Total fair value of available-for-sale marketable securities	17,510,000	15,326,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months	17,510,000	4,603,000
Fair Value - Total	17,510,000	4,603,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months	(32,000)	(1,000)
Unrealized Loss - Total	(32,000)	(1,000)
Mortgage-backed securities | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis		268,000
Unrealized Gains
Unrealized (Losses)		(153,000)
Total fair value of available-for-sale marketable securities		115,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - 12 Months or Greater		116,000
Fair Value - Total		116,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - 12 Months or Greater		(152,000)
Unrealized Loss - Total		(152,000)
Equity securities | Unrestricted
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	4,044,000	4,044,000
Unrealized Gains
Unrealized (Losses)	(651,000)	(1,025,000)
Total fair value of available-for-sale marketable securities	3,393,000	3,019,000
Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than 12 Months		3,019,000
Fair Value - 12 Months or Greater	3,393,000
Fair Value - Total	3,393,000	3,019,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 months		(1,025,000)
Unrealized Loss - 12 Months or Greater	(651,000)
Unrealized Loss - Total	$ (651,000)	$ (1,025,000)