Summarized Quarterly Financial Information—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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 47,988	$ 56,486	$ 60,581	$ 59,966	$ 53,174	$ 55,578	$ 38,076	$ 35,976
Income from operations	478	5,569	10,879	11,323	4,370	1,687	4,109	4,236	28,249	14,402	(130,443)
Income available to common stockholders	$ 1,745	$ 4,671	$ 9,592	$ 10,043	$ 2,291	$ 383	$ 3,662	$ 2,607	$ 26,051	$ 8,943	$ (137,218)
Earnings per share, Basic (in usd per share)	$ 0.03	$ 0.07	$ 0.15	$ 0.15	$ 0.04	$ 0.01	$ 0.06	$ 0.04	$ 0.39	$ 0.14	$ (2.20)
Earnings per share, Diluted (in usd per share)	$ 0.03	$ 0.07	$ 0.15	$ 0.15	$ 0.04	$ 0.01	$ 0.06	$ 0.04	$ 0.39	$ 0.14	$ (2.20)