Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Long-term debt disclosures
Long-term debt	$ 998,525
Unamortized bond premium-senior notes due 2021	3,124
Total Long-term debt	1,001,649	994,525
Revolving credit facility
Long-term debt disclosures
Long-term debt	239,000	385,000
Senior Notes
Long-term debt disclosures
Unamortized bond premium-senior notes due 2021	3,124
Total Long-term debt	762,649	609,525
7.75% senior unsecured notes due 2018
Long-term debt disclosures
Interest rate stated percentage	7.75%
Total Long-term debt	249,525	249,525
7.125% senior unsecured notes due 2021
Long-term debt disclosures
Interest rate stated percentage	7.125%
Total Long-term debt	$ 510,000	$ 360,000
8.125% Senior Notes due 2016
Long-term debt disclosures
Interest rate stated percentage	8.125%