Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Recurring
Fair Value of Financial Instruments
Assets - investment in U.S. Treasury obligations	$ 891	$ 905
Liabilities - long-term debt (carried at amortized cost, Level 2)	300,638	302,000
Level 1 | Recurring
Fair Value of Financial Instruments
Assets - investment in U.S. Treasury obligations	891	905
Level 2 | Recurring
Fair Value of Financial Instruments
Liabilities - long-term debt (carried at amortized cost, Level 2)	300,638	302,000
Carrying Value
Fair Value of Financial Instruments
Assets - investment in U.S. Treasury obligations	891	905
Liabilities - long-term debt (carried at amortized cost, Level 2)	295,248	295,410
Fair Value
Fair Value of Financial Instruments
Assets - investment in U.S. Treasury obligations	891	905
Liabilities - long-term debt (carried at amortized cost, Level 2)	$ 300,638	$ 302,000