Quarterly Results of Operations (unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 104,473	$ 107,480	$ 135,011	$ 193,814	$ 283,110	$ 273,267	$ 259,812	$ 239,034	$ 540,778	$ 1,055,223	$ 960,186
Income (loss) from operations	(65,286)	(17,972)	(75,108)	(8,334)	(48,672)	32,804	21,917	17,935	(166,700)	23,984	(6,229)
Income tax (expense) benefit	23,861	6,682	2,586	4,450	20,198	(9,927)	1,070	(37)	37,579	11,304	19,846
Net income (loss)	$ (48,300)	$ (17,540)	$ (77,281)	$ (12,019)	$ (47,573)	$ 12,453	$ (319)	$ (2,579)	$ (155,140)	$ (38,018)	$ (35,932)
Earnings (loss) per share:
Income (loss) per common share - Basic	$ (0.75)	$ (0.27)	$ (1.20)	$ (0.19)	$ (0.75)	$ 0.20	$ (0.01)	$ (0.04)	$ (2.41)	$ (0.60)	$ (0.58)
Income (loss) per common share - Diluted	$ (0.75)	$ (0.27)	$ (1.20)	$ (0.19)	$ (0.75)	$ 0.19	$ (0.01)	$ (0.04)	$ (2.41)	$ (0.60)	$ (0.58)