Investments and Fair Value Measurements (Details) (USD $)	3 Months Ended		61 Months Ended
	Mar. 31, 2013 days	Mar. 31, 2012	Mar. 31, 2013	Dec. 31, 2012	Feb. 14, 2008
Schedule of Available-for-sale Securities
Basis of Tested Impact on Securities	0.50%		0.50%
Held-to-maturity Securities	$ 1,400,000		$ 1,400,000	$ 1,300,000
Amortized Cost and Fair Value of Investments
Amortized Cost					198,500,000
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value	0		0
Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis	0		0
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	20,016,000	50,569,000
Settlements	(25,000)	(25,000)
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	0	0
Fair value, end of period	19,991,000	50,544,000	19,991,000
Auction Rate Securities, Debt, Rate Setting Interval (in days)	35
Percent of portfolio with AAA credit rating	41.00%		41.00%
Maturity and calls of investments	(25,000)	(25,000)
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(1,284,000)		(1,284,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	0	0
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities			177,200,000
Auction rate security investments percentage of total assets	3.90%		3.90%
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	0.43%		0.43%	0.42%
Investment Inputs Discount Rate	0.27%		0.27%	0.25%
Investment Inputs Liquidity Discount Rate	0.25%		0.25%	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	2.31%		2.31%	2.11%
Investment Inputs Discount Rate	0.94%		0.94%	0.84%
Investment Inputs Liquidity Discount Rate	0.63%		0.63%	0.61%
Available-for-sale Securities [Member]
Amortized Cost and Fair Value of Investments
Amortized Cost	21,275,000		21,275,000
Fair Value	19,991,000		19,991,000
Auction rate student loan educational bonds long-term
Amortized Cost and Fair Value of Investments
Amortized Cost	21,275,000		21,275,000	21,300,000
Gross Unrealized Gains	0		0	0
Gross Unrealized Losses	1,284,000		1,284,000	1,284,000
Fair Value	$ 19,991,000		$ 19,991,000	$ 20,016,000