Selected Quarterly Financial Data Unaudited - Quarterly Financial Information for Interim Periods Subsequent to IPO Closing (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]
Revenue	$ 4,878	$ 13,193	[1]	$ 5,298	$ 5,001	$ 5,583	$ 10,788	$ 5,600	$ 5,385	$ 28,370	$ 27,356	$ 14,308
Income from operations	35	8,661	[1]	1,378	1,032	2,019	6,519	(770)	1,944	11,106	9,712	(3,153)
Net income attributable to common shareholders	$ 1,224	$ 3,595	[1]			$ 2,514	$ 1,319			$ 13,018	$ 3,833	$ (4,301)
Basic net income per common share	$ 0.14	$ 2.67	[1]			$ 1.87	$ 0.99			$ 4.11	$ 2.87	$ (3.24)
Diluted net income per common share	$ 0.13	$ 1.69	[1]			$ 1.17	$ 0.63			$ 3.28	$ 1.91	$ (3.24)

[1] (1) The financial data, including per share amounts, for all interim periods prior to and including the three month period ended September 30, 2014, do not reflect the IPO.