Selected Quarterly Financial Data (Unaudited) (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
Selected Quarterly Financial Data Details
Revenues	$ 66,695	$ 57,200	$ 56,127	$ 44,040	$ 54,451	$ 39,202	$ 36,505	$ 25,434	$ 224,062	$ 155,592	$ 130,644
Operating (loss) income	857	1,351	5,790	(2,948)	10,588	1,769	(9,321)	(4,531)	5,050	(1,495)	(1,124)
Net (loss) income	$ (1,975)	$ (2,146)	$ 1,992	$ (6,576)	$ 7,768	$ (1,087)	$ (12,389)	$ (7,796)
Basic net income (loss) per common and potential common share	$ (0.02)	$ (0.02)	$ 0.02	$ (0.06)	$ 0.08	$ (0.01)	$ (0.13)	$ (0.09)	$ (0.08)	$ (0.14)	$ (0.22)
Diluted net income (loss) per common and potential common share	$ (0.02)	$ (0.02)	$ 0.02	$ (0.06)	$ 0.07	$ (0.01)	$ (0.13)	$ (0.09)	$ (0.08)	$ (0.14)	$ (0.22)