Quarterly Financial Information (Summary of Selected Quarterly Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effect of Fourth Quarter Events [Line Items]
Revenues	$ 118,911	$ 113,767	$ 107,868	$ 105,964	$ 105,443	$ 103,465	$ 98,687	$ 94,768	$ 446,510	$ 402,363	$ 311,083
Operating income	7,553	12,833	10,826	10,915	11,092	8,505	8,225	10,235	42,127	38,057	35,983
Net income (loss)	(16,113)	7,394	4,608	5,568	5,481	6,538	5,807	6,859	1,457	24,685	24,129
Net income (loss) attributable to common shares	$ (14,142)	$ 6,507	$ 4,040	$ 4,877	$ 4,806	$ 5,730	$ 5,100	$ 5,889	$ 1,282	$ 21,525	$ 20,326
Basic (in dollars per share)	$ (0.29)	$ 0.13	$ 0.08	$ 0.10	$ 0.10	$ 0.12	$ 0.11	$ 0.14	$ 0.01	$ 0.47	$ 0.54
Diluted (in dollars per share)	$ (0.29)	$ 0.13	$ 0.08	$ 0.10	$ 0.10	$ 0.12	$ 0.10	$ 0.14	$ 0.01	$ 0.46	$ 0.53
Qualitytech, LP
Effect of Fourth Quarter Events [Line Items]
Revenues	$ 118,911	$ 113,767	$ 107,868	$ 105,964	$ 105,443	$ 103,465	$ 98,687	$ 94,768	$ 446,510	$ 402,363	$ 311,083
Operating income	7,553	12,833	10,826	10,915	11,092	8,505	8,225	10,235	42,127	38,057	35,983
Net income (loss)	$ (16,113)	$ 7,394	$ 4,608	$ 5,568	$ 5,481	$ 6,538	$ 5,807	$ 6,859	$ 1,457	$ 24,685	$ 24,129