Marketable Securities (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Total	$ 422,639,000	$ 321,845,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Total	422,989,000	322,138,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Total	552,000	529,000
Unrealized (Losses) - Total	(202,000)	(236,000)
Unrealized Net - Total	350,000	293,000
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	118,892,000	111,774,000
Fair Value - 12 Months or Greater	117,000	116,000
Fair Value - Total	119,009,000	111,890,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(1,645,000)	(1,108,000)
Unrealized Loss - 12 Months or Greater	(146,000)	(152,000)
Unrealized Loss - Total	(1,791,000)	(1,260,000)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of equity securities	2,400,000	3,000,000
Cost basis of equity securities	4,000,000	4,000,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized (Losses) - Total	(1,600,000)	(1,000,000)
Unrestricted [Member]
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	116,479,000
Fair Value - 12 Months or Greater	117,000
Fair Value - Total	116,596,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(1,642,000)
Unrealized Loss - 12 Months or Greater	(146,000)
Unrealized Loss - Total	(1,788,000)
Unrestricted [Member] | U.S. Government Obligations [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	65,959,000	12,025,000
Amortized Cost Basis - Maturities after one year through five years	285,363,000	272,433,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	66,025,000	12,067,000
Fair Value - Maturities after one year through five years	285,763,000	272,752,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	78,000	42,000
Unrealized Gains - Maturities after one year through five years	437,000	400,000
Unrealized (Losses) - Maturities within one year	(12,000)
Unrealized (Losses) - Maturities after one year through five years	(37,000)	(81,000)
Unrealized Net - Maturities within one year	66,000	42,000
Unrealized Net - Maturities after one year through five years	400,000	319,000
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	89,055,000	103,529,000
Fair Value - Total	89,055,000	103,529,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(49,000)	(81,000)
Unrealized Loss - Total	(49,000)	(81,000)
Unrestricted [Member] | U.S. Government Guaranteed Corporate Bonds [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	50,635,000	15,263,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	50,654,000	15,316,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	23,000	53,000
Unrealized (Losses) - Maturities within one year	(4,000)
Unrealized Net - Maturities within one year	19,000	53,000
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	24,969,000
Fair Value - Total	24,969,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(4,000)
Unrealized Loss - Total	(4,000)
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
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year		622,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized (Losses) - Maturities within one year		(1,000)
Unrealized Net - Maturities within one year		(1,000)
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)
Unrealized Loss - Total		(1,000)
Unrestricted [Member] | Municipal Bonds [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	12,385,000	15,314,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	12,386,000	15,326,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	1,000	13,000
Unrealized (Losses) - Maturities within one year		(1,000)
Unrealized Net - Maturities within one year	1,000	12,000
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] | Equity Securities [Member]
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	2,455,000	3,019,000
Fair Value - Total	2,455,000	3,019,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(1,589,000)	(1,025,000)
Unrealized Loss - Total	(1,589,000)	(1,025,000)
Unrestricted [Member] | Mortgage-Backed Securities [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities after one year through five years	102,000	104,000
Amortized Cost Basis - Maturities after five years through ten years	161,000	164,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities after one year through five years	29,000	28,000
Fair Value - Maturities after five years through ten years	88,000	87,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized (Losses) - Maturities after one year through five years	(73,000)	(76,000)
Unrealized (Losses) - Maturities after five years through ten years	(73,000)	(77,000)
Unrealized Net - Maturities after one year through five years	(73,000)	(76,000)
Unrealized Net - Maturities after five years through ten years	(73,000)	(77,000)
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - 12 Months or Greater	117,000	116,000
Fair Value - Total	117,000	116,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - 12 Months or Greater	(146,000)	(152,000)
Unrealized Loss - Total	(146,000)	(152,000)
Unrestricted [Member] | Debt Securities [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	128,979,000	43,225,000
Amortized Cost Basis - Maturities after one year through five years	285,465,000	272,537,000
Amortized Cost Basis - Maturities after five years through ten years	161,000	164,000
Amortized Cost Basis - Total	414,605,000	315,926,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	129,065,000	43,331,000
Fair Value - Maturities after one year through five years	285,792,000	272,780,000
Fair Value - Maturities after five years through ten years	88,000	87,000
Fair Value - Total	414,945,000	316,198,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	102,000	108,000
Unrealized Gains - Maturities after one year through five years	437,000	400,000
Unrealized Gains - Total	539,000	508,000
Unrealized (Losses) - Maturities within one year	(16,000)	(2,000)
Unrealized (Losses) - Maturities after one year through five years	(110,000)	(157,000)
Unrealized (Losses) - Maturities after five years through ten years	(73,000)	(77,000)
Unrealized (Losses) - Total	(199,000)	(236,000)
Unrealized Net - Maturities within one year	86,000	106,000
Unrealized Net - Maturities after one year through five years	327,000	243,000
Unrealized Net - Maturities after five years through ten years	(73,000)	(77,000)
Unrealized Net - Total	340,000	272,000
Restricted [Member]
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	2,413,000
Fair Value - Total	2,413,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(3,000)
Unrealized Loss - Total	(3,000)
Restricted [Member] | U.S. Government Obligations [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Maturities within one year	3,847,000	3,347,000
Amortized Cost Basis - Maturities after one year through five years	4,187,000	2,572,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Maturities within one year	3,853,000	3,357,000
Fair Value - Maturities after one year through five years	4,191,000	2,583,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Maturities within one year	6,000	10,000
Unrealized Gains - Maturities after one year through five years	7,000	11,000
Unrealized (Losses) - Maturities after one year through five years	(3,000)
Unrealized Net - Maturities within one year	6,000	10,000
Unrealized Net - Maturities after one year through five years	4,000	11,000
Continuous Unrealized Loss Position, Fair Vaue [Abstract]
Fair Value - Less than 12 Months	2,413,000
Fair Value - Total	2,413,000
Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Unrealized Loss - Less than 12 Months	(3,000)
Unrealized Loss - Total	(3,000)
Restricted [Member] | Debt Securities [Member]
Debt Maturities, Amortized Cost Basis [Abstract]
Amortized Cost Basis - Total	8,034,000	5,919,000
Debt Maturities, Fair Value [Abstract]
Fair Value - Total	8,044,000	5,940,000
Unrealized Gains (Losses), Net [Abstract]
Unrealized Gains - Total	13,000	21,000
Unrealized (Losses) - Total	(3,000)
Unrealized Net - Total	$ 10,000	$ 21,000