Marketable Securities (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	$ 111,774,000	$ 369,215,000
Fair Value - 12 Months or Greater	116,000	1,128,000
Fair Value - Total	111,890,000	370,343,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(1,108,000)	(2,227,000)
Unrealized Loss - 12 Months or Greater	(152,000)	(141,000)
Unrealized Loss - Total	(1,260,000)	(2,368,000)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of equity securities	3,000,000	3,600,000
Cost basis of equity securities	4,000,000	4,000,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized (Losses) - Total	(1,000,000)	(400,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	3,019,000	3,612,000
Fair Value - Total	3,019,000	3,612,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(1,025,000)	(433,000)
Unrealized Loss - Total	(1,025,000)	(433,000)
Debt Securities [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Total	321,845,000	511,625,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Total	322,138,000	510,276,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Total	529,000	586,000
Unrealized (Losses) - Total	(236,000)	(1,935,000)
Unrealized Net - Total	293,000	(1,349,000)
Unrestricted [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	43,225,000	136,307,000
Amortized Cost Basis - Maturities after one year through five years	272,537,000	367,977,000
Amortized Cost Basis - Maturities after five years through ten years	164,000	284,000
Amortized Cost Basis - Total	315,926,000	504,568,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	43,331,000	136,796,000
Fair Value - Maturities after one year through five years	272,780,000	366,198,000
Fair Value - Maturities after five years through ten years	87,000	243,000
Fair Value - Total	316,198,000	503,237,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	108,000	522,000
Unrealized Gains - Maturities after one year through five years	400,000	64,000
Unrealized Gains - Total	508,000	586,000
Unrealized (Losses) - Maturities within one year	(2,000)	(33,000)
Unrealized (Losses) - Maturities after one year through five years	(157,000)	(1,843,000)
Unrealized (Losses) - Maturities after five years through ten years	(77,000)	(41,000)
Unrealized (Losses) - Total	(236,000)	(1,917,000)
Unrealized Net - Maturities within one year	106,000	489,000
Unrealized Net - Maturities after one year through five years	243,000	(1,779,000)
Unrealized Net - Maturities after five years through ten years	(77,000)	(41,000)
Unrealized Net - Total	272,000	(1,331,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months		363,061,000
Fair Value - 12 Months or Greater		1,128,000
Fair Value - Total		364,189,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months		(2,209,000)
Unrealized Loss - 12 Months or Greater		(141,000)
Unrealized Loss - Total		(2,350,000)
Unrestricted [Member] | U.S. Government Obligations [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	12,025,000	83,635,000
Amortized Cost Basis - Maturities after one year through five years	272,433,000	352,345,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	12,067,000	83,684,000
Fair Value - Maturities after one year through five years	272,752,000	350,683,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	42,000	54,000
Unrealized Gains - Maturities after one year through five years	400,000	64,000
Unrealized (Losses) - Maturities within one year		(5,000)
Unrealized (Losses) - Maturities after one year through five years	(81,000)	(1,726,000)
Unrealized Net - Maturities within one year	42,000	49,000
Unrealized Net - Maturities after one year through five years	319,000	(1,662,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	103,529,000	340,444,000
Fair Value - Total	103,529,000	340,444,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(81,000)	(1,731,000)
Unrealized Loss - Total	(81,000)	(1,731,000)
Unrestricted [Member] | U.S. Government Guaranteed Corporate Bonds [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	15,263,000	48,173,000
Amortized Cost Basis - Maturities after one year through five years		15,522,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	15,316,000	48,531,000
Fair Value - Maturities after one year through five years		15,477,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	53,000	358,000
Unrealized (Losses) - Maturities after one year through five years		(45,000)
Unrealized Net - Maturities within one year	53,000	358,000
Unrealized Net - Maturities after one year through five years		(45,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months		19,005,000
Fair Value - 12 Months or Greater		19,005,000
Unrestricted [Member] | U.S. Government Guaranteed Collateralized Mortgage Obligations [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	623,000	2,027,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	622,000	2,131,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year		104,000
Unrealized (Losses) - Maturities within one year	(1,000)
Unrealized Net - Maturities within one year	(1,000)	104,000
Continuous Unrealized Loss Position, Fair Vaue [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)	(45,000)
Unrealized Loss - Total	(1,000)	(45,000)
Unrestricted [Member] | Municipal Bonds [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	15,314,000	1,597,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	15,326,000	1,603,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	13,000	6,000
Unrealized (Losses) - Maturities within one year	(1,000)
Unrealized Net - Maturities within one year	12,000	6,000
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	4,603,000
Fair Value - Total	4,603,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(1,000)
Unrealized Loss - Total	(1,000)
Unrestricted [Member] | Mortgage-Backed Securities [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year		875,000
Amortized Cost Basis - Maturities after one year through five years	104,000	110,000
Amortized Cost Basis - Maturities after five years through ten years	164,000	284,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year		847,000
Fair Value - Maturities after one year through five years	28,000	38,000
Fair Value - Maturities after five years through ten years	87,000	243,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized (Losses) - Maturities within one year		(28,000)
Unrealized (Losses) - Maturities after one year through five years	(76,000)	(72,000)
Unrealized (Losses) - Maturities after five years through ten years	(77,000)	(41,000)
Unrealized Net - Maturities within one year		(28,000)
Unrealized Net - Maturities after one year through five years	(76,000)	(72,000)
Unrealized Net - Maturities after five years through ten years	(77,000)	(41,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - 12 Months or Greater	116,000	1,128,000
Fair Value - Total	116,000	1,128,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - 12 Months or Greater	(152,000)	(141,000)
Unrealized Loss - Total	(152,000)	(141,000)
Restricted [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Total	5,919,000	7,057,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Total	5,940,000	7,039,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Total	21,000
Unrealized (Losses) - Total		(18,000)
Unrealized Net - Total	21,000	(18,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months		6,154,000
Fair Value - Total		6,154,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months		(18,000)
Unrealized Loss - Total		(18,000)
Restricted [Member] | U.S. Government Obligations [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	3,347,000	2,922,000
Amortized Cost Basis - Maturities after one year through five years	2,572,000	4,135,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	3,357,000	2,921,000
Fair Value - Maturities after one year through five years	2,583,000	4,118,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	10,000
Unrealized Gains - Maturities after one year through five years	11,000
Unrealized (Losses) - Maturities within one year		(1,000)
Unrealized (Losses) - Maturities after one year through five years		(17,000)
Unrealized Net - Maturities within one year	10,000	(1,000)
Unrealized Net - Maturities after one year through five years	11,000	(17,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months		6,154,000
Fair Value - Total		6,154,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months		(18,000)
Unrealized Loss - Total		$ (18,000)