Investments and Fair Value Measurements (Details) (USD $)	12 Months Ended			59 Months Ended
	Dec. 31, 2012 days	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Feb. 14, 2008
Schedule of Available-for-sale Securities
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	$ 1,797,000	$ 0	$ 2,245,000
Amortized Cost and Fair Value of Investments
Amortized Cost					198,500,000
Fair Value	20,000,000	50,600,000		20,000,000
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	25,000			25,000
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	25,000			25,000
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value	0			0
Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis	0			0
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value	0			0
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	0			0
Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value	19,991,000			19,991,000
Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis	21,275,000			21,275,000
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	50,569,000	88,694,000
Settlements	(32,350,000)	(38,125,000)
Purchases	0	0
Issuances	0	0
Sales	0	0
Transfers in to (out of) Level 3	0	0
Total gains or losses (realized/unrealized) included in earnings	0	0
Total gains or losses (realized/unrealized) included in other comprehensive income, net of tax	1,797,000	0
Fair value, end of period	20,016,000	50,569,000	88,694,000	20,016,000
Auction Rate Securities, Debt, Rate Setting Interval (in days)	35
Percent of portfolio with AAA credit rating	41.00%	100.00%		41.00%
Maturity and calls of investments	(32,350,000)	(38,125,000)
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(1,300,000)			(1,300,000)
Basis of Tested Impact on Securities	0.50%			0.50%
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	0	0	0
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	32,400,000			177,200,000
Auction rate security investments percentage of total assets	4.30%			4.30%
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investment Inputs Average Life of Underlying Loans	2	2		2
Investment Inputs Rate of Return	0.42%	0.68%		0.42%
Investment Inputs Discount Rate	0.25%	0.48%		0.25%
Investment Inputs Liquidity Discount Rate	0.17%	0.55%		0.17%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investment Inputs Average Life of Underlying Loans	12	12		12
Investment Inputs Rate of Return	2.11%	2.92%		2.11%
Investment Inputs Discount Rate	0.84%	1.14%		0.84%
Investment Inputs Liquidity Discount Rate	0.61%	1.16%		0.61%
Available-for-sale Securities [Member]
Amortized Cost and Fair Value of Investments
Amortized Cost	21,300,000			21,300,000
Fair Value	20,016,000			20,016,000
Auction rate student loan educational bonds long-term
Amortized Cost and Fair Value of Investments
Amortized Cost	21,300,000	53,650,000		21,300,000
Gross Unrealized Gains	0	0		0
Gross Unrealized Losses	1,284,000	3,081,000		1,284,000
Fair Value	$ 20,016,000	$ 50,569,000		$ 20,016,000