Supplemental Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 94,673	$ 119,283	$ 129,895	$ 124,605	$ 112,267	$ 111,165	$ 98,916	$ 106,867	$ 468,456	$ 429,215
Operating income	(3,244)	45,565	34,739	34,579	24,577	33,918	5,003	(50,883)	111,639	12,615	79,793
Net income (loss)	$ (4,267)	$ 27,429	$ 9,327	$ 11,392	$ 6,425	$ 10,951	$ (1,029)	$ (41,209)	$ 43,881	$ (24,862)
Net income (loss) per common share:
Basic (in dollars per share)	$ (0.35)	$ 2.25	$ 0.77	$ 0.94	$ 0.53	$ 0.90	$ (0.08)	$ (3.39)	$ 3.61	$ (2.04)	$ 2.89
Diluted (in dollars per share)	$ (0.35)	$ 2.25	$ 0.77	$ 0.94	$ 0.53	$ 0.90	$ (0.08)	$ (3.39)	$ 3.61	$ (2.04)	$ 2.89
Weighted average common shares outstanding:
Basic (in shares)	12,170	12,166	12,166	12,166	12,165	12,165	12,165	12,165	12,167	12,165	12,164
Diluted (in shares)	12,170	12,166	12,166	12,166	12,165	12,165	12,165	12,165	12,167	12,165	12,164