Long-term debt Long-Term Debt--Senior Notes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended									12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Senior Notes	Dec. 31, 2012 Senior Notes	Dec. 31, 2011 Senior Notes	Dec. 31, 2013 Senior Notes 9.875% Senior Notes due 2020	Dec. 31, 2013 Senior Notes 8.25% Senior Notes due 2021	Feb. 22, 2011 Senior Notes 8.25% Senior Notes due 2021	Dec. 31, 2013 Senior Notes 7.625% Senior Notes due 2022	Nov. 15, 2012 Senior Notes 7.625% Senior Notes due 2022	May 02, 2012 Senior Notes 7.625% Senior Notes due 2022	Dec. 31, 2012 Senior Notes 8.875% Senior Notes Due 2017	May 02, 2012 Senior Notes 8.875% Senior Notes Due 2017	Dec. 31, 2011 Senior Notes 8.5% Senior Notes Due 2015	Feb. 22, 2011 Senior Notes 8.5% Senior Notes Due 2015
Debt Instrument [Line Items]
Senior Notes, stated interest rate							9.875%	8.25%	8.25%	7.625%	7.625%	7.625%		8.875%		8.50%
Maturity date (year)							2020	2021		2022
Net amortization of (premium) discount				$ (387)	$ 439	$ 668
Redemption price at change of control event, as a percentage of principal				101.00%
Aggregate principal amount									400,000		150,000	400,000
Loss on extinguishment of debt	$ 0	$ (21,714)	$ (20,592)										$ (21,714)		$ (20,592)
Maturity date								Sep. 01, 2021		Nov. 15, 2022