Marketable Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Security	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Number of securities sold	2
Amortized Cost Basis	$ 226,427	$ 0
Unrealized Gain	966	0
Total Estimated Fair Value	227,393	0
Amortized Cost Basis Rollforward
Marketable securities beginning balance	0
Face value of marketable securities acquired	235,000
Premiums and discounts on purchase of marketable securities, net of acquisition costs	8,444
Amortization on marketable securities	(713)
Sales of securities and realized gain	(16,304)
Marketable securities ending balance	226,427	0
Unrealized Gain Rollforward
Marketable securities beginning balance	0	0
Sales of securities and realized gain	(141)	0
Increase in fair value of marketable securities	1,107
Marketable securities ending balance	966	0
Fair Value Rollforward
Marketable securities beginning balance	0
Face value of marketable securities acquired	235,000
Premiums and discounts on purchase of marketable securities, net of acquisition costs	8,444
Amortization on marketable securities	(713)
Sales of securities and realized gain	(16,445)
Increase in fair value of marketable securities	1,107
Marketable securities ending balance	227,393	0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Due within one year	5,001
Due after one year through five years	184,410
Due after five years through ten years	37,016
Due after ten years	0
Total Amortized Cost Basis	226,427
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Due within one year	5,001
Due after one year through five years	185,385
Due after five years through ten years	37,007
Due after ten years	0
Total Estimated Fair Value	227,393	0
U.S. Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	40,104
Unrealized Gain	159
Total Estimated Fair Value	40,263
Amortized Cost Basis Rollforward
Marketable securities ending balance	40,104
Unrealized Gain Rollforward
Marketable securities ending balance	159
Fair Value Rollforward
Marketable securities ending balance	40,263
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Total Estimated Fair Value	40,263
U.S. Agency Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	50,401
Unrealized Gain	205
Total Estimated Fair Value	50,606
Amortized Cost Basis Rollforward
Marketable securities ending balance	50,401
Unrealized Gain Rollforward
Marketable securities ending balance	205
Fair Value Rollforward
Marketable securities ending balance	50,606
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Total Estimated Fair Value	50,606
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	135,922
Unrealized Gain	602
Total Estimated Fair Value	136,524
Amortized Cost Basis Rollforward
Marketable securities ending balance	135,922
Unrealized Gain Rollforward
Marketable securities ending balance	602
Fair Value Rollforward
Marketable securities ending balance	136,524
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Total Estimated Fair Value	$ 136,524