Debt Schedule of Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term Debt	$ 205,307	$ 237,109
Long-term Debt, net of deferred financing costs	204,671	236,429
Loan Agreement
Debt Instrument [Line Items]
Long-term Debt	105,307	137,109
Less unamortized deferred financing fees
Debt Instrument [Line Items]
Less unamortized deferred financing fees	636	680
Four Point Six Seven Percent Senior Unsecured Notes Due Twenty Twenty One [Member] | Less unamortized deferred financing fees
Debt Instrument [Line Items]
Long-term Debt	40,000	40,000
Interest rate	4.67%
Five Point Two Five Percent Senior Unsecured Notes Due Twenty Twenty Four [Member] | Less unamortized deferred financing fees
Debt Instrument [Line Items]
Long-term Debt	11,000	11,000
Interest rate	5.25%
Five Point Three Zero Percent Senior Unsecured Notes Due Twenty Twenty Four [Member] | Less unamortized deferred financing fees
Debt Instrument [Line Items]
Long-term Debt	29,000	29,000
Interest rate	5.30%
Five Point Four Five Percent Senior Unsecured Notes Due Twenty Twenty Six [Member] | Less unamortized deferred financing fees
Debt Instrument [Line Items]
Long-term Debt	$ 20,000	$ 20,000
Interest rate	5.45%