Quarterly Operating Results (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]
Total revenue	$ 67,548	$ 78,229	$ 72,257	$ 58,916	$ 52,610	$ 60,662	$ 47,077	$ 36,866	$ 276,950	$ 197,216	$ 126,228
Total operating expenses	58,634	58,115	54,191	50,487	48,095	45,979	42,076	34,370	221,427	170,520	108,867
Operating income	8,914	20,114	18,066	8,429	4,516	14,683	5,001	2,496	55,523	26,696	17,361
Net income attributable to common shareholders	$ 4,477	$ 14,315	$ 12,763	$ 1,411	$ (5,660)	$ 8,664	$ 65,137	$ (1,808)	$ 32,815	$ 66,333	$ 2,688
Income (loss) per common share, basic (in dollars per share)	$ 0.12	$ 0.37	$ 0.33	$ 0.04	$ (0.16)	$ 0.32	$ 2.46	$ (0.07)	$ 0.87	$ 2.32	$ 0.13
Income (loss) per common share, diluted (in dollars per share)	$ 0.12	$ 0.37	$ 0.33	$ 0.04	$ (0.16)	$ 0.31	$ 2.44	$ (0.07)	$ 0.86	$ 2.30	$ 0.13
Weighted average number of common shares outstanding:
Basic (in shares)	38,213,219	38,212,028	38,211,833	37,018,039	33,972,134	27,370,815	26,437,878	26,271,678	37,917,871	28,531,094	21,035,892
Diluted (in shares)	38,619,472	38,614,360	38,618,824	37,322,278	33,972,134	27,695,347	26,734,919	26,271,678	38,322,285	28,846,724	21,283,831