CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net income (loss)	$ 24,000	$ 60,265	$ (75,192)	$ (78,909)	$ 128,771	$ 19,123	$ 56,507	$ 74,969	$ (69,836)	$ 279,370	$ (91,044)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Deferred income taxes									110,786	216,409	82,380
Gain on sale of assets									(24,651)	(23,769)
Loss on extinguishment of debt									165	2,898
Financing activities
Cash and cash equivalents at beginning of period				$ 554,831				$ 598,108	554,831	598,108	515,164
Cash and cash equivalents at end of period	$ 275,004				$ 554,831				$ 275,004	$ 554,831	$ 598,108